Add shapes, the Insert tab, and an optional Insert button on the toolbar

[marcosqlbi]

Pull request 3 of the 1.6.0 plan in docs/design-objects.md, closing #130. It adds the
eight shapes, the Insert tab they come from, and the two Toolbar preferences that decide
where the Insert tools live and what happens after one has been drawn. It builds on #135,
which moved the per-type questions onto the records themselves — this adds a record and a
geometry and touches almost none of the window's switches.

Why it is shaped this way

A shape is taken hold of by its outline, never by its interior (decision 11). That is
the whole reason a shape can be a container: ink drawn inside one links to it and travels
with it, and a tap in the middle still reaches whatever is drawn there. The band is the
same eight screen pixels a frame's edge uses.

One description of the outline serves everybody. Core.Geometry.ShapeGeometry returns
a shape's outline as a start point and a list of line and arc steps. The surface hands the
arcs straight to WPF, so a circle stays a circle at any zoom; the hit test and the area
tests walk the same outline flattened to a polygon, sixty-four points to a full circle.
Nothing derives the geometry a second time, which is what stops the renderer and the hit
test disagreeing about where a shape's edge is — and it is what pull request 6 will read
to write native PowerPoint and PDF geometry.

The area asks the outline too. A rubber band over the empty corner of an ellipse's box
does not take the ellipse; one that crosses the curve does. A box test would have been
cheaper and would have felt wrong for exactly the shapes people draw around things.

Version 7 is asked for by the board that needs it. NeedsVersion7 is a one-line
predicate the label and connector work extends; a board with only frames still writes as 6
and one with neither as 5, so a board keeps opening in the release that can read it.

The two "applies when" tests in the property bar are named statics. HasPrimaryColor
and HasThickness are each one line for the text and connector pull requests to extend,
rather than a predicate repeated at every row. Applying a color, a thickness, or a fill
replaces every selected stroke and shape as one step and becomes what the next shape is
drawn with.

Free resize is the one thing a shape does differently. Its corner handle takes the
width and the height the pointer is at, and Shift keeps the aspect — the opposite way round
from a picture, which is aspect-locked. It applies only when the selection is exactly one
shape; a set still scales as a set.

The editable export keeps the shapes visible. The overlay picture now carries the ink
and the shapes, and the vector PDF path — which draws the ink itself — still gets an
overlay for the shapes alone. Native shapes are pull request 6; until then nothing
disappears from a deck.

The toolbar's width

Measured from the XAML for the floating palette, at the default where the Eraser is not on
the bar. With the preference off both new controls are Collapsed and contribute nothing,
so the width is the 1.5.2 width to the pixel.

Layout	Insert and Lasso on the toolbar off	on
Compact (Chevron or Icons beside the size chips)	140	202
Dual palette (the default)	286	310

The compact pair grows by the Insert button (42) and the Select chevron (20); the dual pair
by 24, which is what the Insert button adds to the shared color column that sets the
palette's width. Both pairs were confirmed against a running copy: the measured deltas are
62 and 24 exactly. With the Eraser on the bar — that is, with finger or mouse drawing on —
the compact pair is 182 and 244.

Decisions the plan did not settle

• The shape defaults start at the pen's defaults, not at the live pen. Decision 5 says
  a shape's first outline color and thickness are "the current pen's". Reading the pen's
  setting at the moment a shape is drawn would make the same gesture produce different
  shapes depending on which color was last chosen for ink, so ShapeSettings instead
  starts at InkPalettes.DefaultPen (vermillion, 4) and is last-used from then on, which
  is what the settings table asks for.
• Proportional corners and slants. A rounded rectangle's radius is a fifth of its short
  side, a parallelogram slants by a quarter of its width, a block arrow's head starts at
  three fifths and its shaft is half the height. Proportional rather than absolute, so a
  shape dragged larger keeps the look it had when it was drawn.
• The pentagon fills its box rather than being inscribed in a circle inside it: a shape
  dragged out of a rectangle should occupy that rectangle.
• The Insert row is sticky, which is what Add text labels: click to type on the board #136 settled while this was in flight:
  picking a tool is the start of drawing with it, and the row is where the next one comes
  from. This branch had it closing on a pick and took main's answer instead.
• The Select chevron is in the compact layouts only. The plan names the Insert button
  for the Dual palette layout and says nothing about the chevron there; the dual palette's
  widths are set by a shared column and a chevron would disturb it for one setting. Lasso
  stays reachable from the Edit row in every layout.
• The glyphs are drawn by hand, as the plan allows: Fluent UI System Icons has no
  outline shape set. Each is two nested contours filled even-odd on the same 24-unit grid,
  including the Insert button's.
• Alt+I opens the Insert tab. F, E, V and H were taken.
• Ctrl+C with one shape selected still copies nothing, as it does for a frame today.
  Decision 12 names a text container and a picture as the single-object cases and sends
  everything else through the rasterizer only when more than one thing is selected. Worth a
  look when the native export lands.

Taking in the text labels (#136)

origin/main was merged in after #136 landed, so the two sit side by side rather than in
two places:

• One Insert tab and one row: the eight shapes, a separator, then Text, which is the
  order the flyout shows and the order the connectors will be inserted into.
• NeedsVersion7 covers labels and shapes; the archive keeps both cases and both sets of
  DTO fields.
• The property bar's tests now read: Color for a stroke, a shape, or a label; Thickness for
  a stroke or a shape; Fill for a shape; Font for a label. A color reaches strokes and
  shapes as one step, and labels through their own path — the one that also changes the box
  being typed into while a label is open.
• The overlay picture carries the ink, the labels, and the shapes, and the vector path
  still emits one for the design objects alone.
• After inserting an object now governs the Text tool too. It was written for the
  shapes, but decision 3 is about every Insert tool, so a committed label either leaves the
  tool for the next click or hands it back to Select.
• The toolbar's Insert flyout ends with Text, and the Insert button reads as on for either
  tool.

Tests

Core harness: the outline of every kind at a known box; the band hitting the outline and
missing both the middle and the outside, and narrowing with the zoom; an area taking a
shape by its outline under both rules and refusing an empty corner of its box; a stroke
touching only a shape linking to it; the archive round trip with and without a fill, the
three versions, and an unknown kind normalizing to a rounded rectangle; the round trip and
normalization of both Toolbar settings and the shape defaults.

To try by hand

• Draw each of the eight from the Insert tab with the pen, and with a finger under Finger
  drawing. Only a mouse was driven here.
• Shift while dragging one out, for the square.
• Tap without dragging, for the 160 x 120 shape at the tap.
• Turn on Insert and Lasso on the toolbar and check the flyout and the Select chevron
  with a pen, which reaches them through the palette's own stylus path rather than through
  mouse promotion.
• Compare the toolbar's width against 1.5.2 with the preference off, in both layouts.
• Draw ink inside a shape, move the shape, and check the ink comes with it.
• Set After inserting an object to Return to Select and draw one.
• Export a board with shapes to an editable deck and to a PDF, and check they are in both.
• A drag that is long in one direction and flat in the other makes a shape with almost no
  height. It is what was dragged and Ctrl+Z removes it, but it is worth a look before the
  connectors land on top of it.

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