Sketch overlap merge, status toasts, curve segment angle, and Add bone options

[trailcode]

Summary

• Closes overlapping / duplicate sketch edges: the sketch splits at overlap ends and keeps each atomic piece once. Fixes a TKGeomBase access violation when a new circle coincided with an existing arc (for example a bone end-cap).
• Status toasts are colored by kind (success, info, constraint, warning, error). Scripts: ezy.msg(text [, kind]). Add bone uses info for the next click, amber for rejected input, green on commit, and red if create fails.
• Settings -> View presentation -> Curve segment angle (gui.curve_deviation_angle_deg, 2-20, default 6) controls AIS curve tessellation. Shared face-mesh polygons are force-cleaned so sketch arcs actually follow the slider.
• Add bone follow-ups: live length dim and Tab-able measure segments, axis-tangent snap to match radius 2, Options for radius and total-length nodes, then exit to Sketch inspection.

Fixes #263

Test plan

• Build Debug EzyCad / EzyCad_tests.
• Run EzyCad_tests (overlap cases in skt_topo_tests).
• Draw the same line or circle twice; add a collinear / same-circle overlap; add a circle on an existing bone end-cap arc (no crash, no stacked copy).
• Drag Curve segment angle between 2 and 20 on a sketch circle (faces on).
• Add bone: info toasts through the clicks, amber on reject, green on commit; radius snap on the second circle; Options persist.
• Review docs/usage-sketch.md, docs/usage-settings.md, docs/usage-occt-view.md, docs/scripting.md, CHANGELOG [Unreleased].

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Note

Medium Risk
Sketch edge add/merge and undo recording touch core planar graph behavior; OCCT tessellation redisplay is broad but display-only. Add-bone flow changes are localized to sketch tools.

Overview
This PR tightens 2D sketch topology so collinear and same-circle overlaps no longer duplicate edges: existing geometry splits at overlap ends, only new atomic pieces are added, and undo records stored arc/line pieces so undo does not drop untouched spans or no-op redraws. That also fixes a TKGeomBase crash when a new circle sat on an existing arc (e.g. bone end-cap).

Status toasts are no longer always red: Status_msg kinds drive color, GUI::show_status maps Result_status (user errors → amber constraint), and ezy.msg(text [, kind]) is wired through Lua/Python. Many call sites switch from plain show_message to typed toasts.

View presentation adds gui.curve_deviation_angle_deg (2–20°, default 6): Occt_view::apply_curve_deviation pushes AIS tessellation to the context and shapes, with extra cleanup so sketch wireframe arcs follow the slider instead of stale face polygons.

Add bone gains persisted radius and total-length node options, temporary measure segments for Tab entry, axis-tangent snap on the second circle while placing radius 1, Holes → None after the waist commits the outline (and hole handlers are skipped when holes are off), and kind-aware progress toasts.

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