Replace the side-panel Inspector tree with a tabbed Inspector that needs no server support

[ericwinger]

Fixes #508

The Enhanced Inspector needs its server-side payload installed and a stone at 3.7.5 or later,
so on a 3.6.x stone Inspect It fell back to a read-only tree in the sidebar no matter what was
installed. That tree is removed outright, along with its Remove and Clear All commands, and
replaced by a basic Inspector that opens as an editor tab in the Enhanced Inspector's own idiom —
tabs over a miller-column strip — built entirely on GCI primitives and kernel sends, so it needs
no server support and works back to 3.6.2.

The Enhanced Inspector is untouched: routeInspect keeps its existing rule, and the only file it
shares in this change is the Meta-tab scroll fix, which it had the same bug in.

What it does

An object gets only the tabs its structure warrants: Slots, Items or Entries,
Bytes, Print, Meta and Evaluate.

• Double-click a row to open that object to the right; Enter dives in place. Each column carries
  its own Back/Forward.
• A row's context menu copies its printString or OOP, browses its class, and edits its value
  through instVarAt:put:, at:put: or a dictionary key, with a revert to the value from before
  the first edit.
• Slots list alphabetically, sorted by clicking the Name column. Each row keeps the
  instVarAt: index it was read at, so sorting cannot misdirect a write, and declaration order —
  what allInstVarNames answers — is that index ascending.
• Meta shows the class name and an info bar of superclass, package and OOP, then sub-tabs for
  instance methods, class methods, definition and comment.
• The Evaluate pane answers to the editor's own Ctrl+K D / E / I for Display, Execute and Inspect
  It, and lists the names in scope beside the expression: the receiver, then every instance
  variable grouped under the class that declares it. Debug It is absent — it works by compiling
  with the single-step flag set, and the pane's evaluateInContext:symbolList: runs to
  completion, leaving no halted process to attach to.
• Every paged tab offers Load all beside Load more, bounded at 50 pages a click so a
  million-element collection cannot hold the session; the tab keeps showing a remainder and
  another click carries on.
• Panels are tracked per session and disposed together when that session logs out — the
  replacement for the tree's per-session root removal.

The column strip both inspectors were growing separately is now one module,
client/src/webview/millerColumns.js, which owns order, insert-right drilling, close, focus and
width; each inspector supplies what is drawn inside a column.

Acceptance criteria

• The side-panel inspector presents an object as tabs, in the Enhanced Inspector's visual
  idiom.
• Works against a stone with no server support installed, including 3.6.x, using only GCI
  primitives.
• Every capability of the classic tree still works or has a stated replacement — multiple
  roots become multiple editor tabs, per-session logout disposal replaces per-session root
  removal, and the arrival badge/status-bar flash is replaced by the tab opening.
• The Enhanced Inspector keeps working exactly as it does today.

Follow-ups

The wish-list items in #508 that are not in this change are collected in #564 — structural
editing of collections and dictionaries, search/filter within a tab, multi-select, dynamic
instance variables, inspecting a dictionary key separately from its value, and a status line.

Testing

• npx vitest run src/basicInspector — 185 tests across 3 files, all passing.
• tsc -p client --noEmit and eslint client/src/basicInspector both clean.
• Coverage was measured by recording every function entry across a run rather than assumed; the
  two paths no test reached — dive and the fetchObjectMeta wrapper — now have tests.
• Exercised by hand against a live stone.

🤖 Generated with Claude Code

[github-advanced-security]

CodeQL found more than 20 potential problems in the proposed changes. Check the Files changed tab for more details.

[ericwinger]

CodeQL's 30 alerts were one finding reached by 30 paths, and it was right. Fixed in bb8425c.

The column strip indexed its columns in a plain {}, and Columns.get(id) is handed ids that
come from outside the model — a host message's columnId, and colEl.dataset.colId in
columnOf. Ask a plain object for __proto__ and it hands back Object.prototype, so the very
next line in populateColumn — col.oop = …, col.title = …, and twenty-eight more — would
have written a column's worth of fields onto the prototype of every object in the frame. Each of
those assignments is what CodeQL flagged, which is why one map produced thirty alerts.

columnsById is now Object.create(null), which answers undefined for those keys; every
caller already treats undefined as "no such column" and returns. The three per-column maps
keyed off the same messages get the same treatment — tabData and loadedRows by tab name,
methodSource by selector — in both the place that seeds them and the place that resets them.

No behavior change: these are lookup tables, nothing iterates them expecting inherited keys, and
the module's only hasOwnProperty is the guarded Object.prototype.hasOwnProperty.call form
against a different object.

Three tests pin it in millerColumns.test.ts, at the model rather than in this inspector, so it
holds for the Enhanced Inspector's strip too: a prototype key answers undefined, a child
message naming __proto__ as its source appends at the far right and leaves bystander objects
clean, and a real id still finds its column.

Worth noting for anyone reading the check history: this push is also the first time the
Health Check workflow ran on this PR. The branch was conflicting with main, so GitHub could
not build the merge ref the pull_request trigger needs, and CodeQL — which analyzes
refs/pull/565/head instead — was the only thing that ran. The merge with main in bb8425c
conflicted only in CHANGELOG.md, where both sides had appended to Added and to Fixed; both sets
of entries are kept.