feat(#464): disambiguate colliding tab origins

[BorisTyshkevich]

What & why

Closes #464.

Same-named Workbench tabs now expose their source without widening every tab:

• collision groups receive compact, minimally unique Dashboard, Library, or
  Draft badges;
• Dashboard source stays derived from the canonical Separate Library queries from dashboard-owned query copies #427 ownership graph, while
  Dashboard-variable tabs use their existing document binding;
• each selectable tab implements the ARIA tab keyboard model with roving focus,
  focus handoff after activation/close, and a full <source> / <document>
  tooltip;
• accessible names expose unsaved, externally changed, and externally deleted
  states, while source abbreviations remain intact for Unicode graphemes;
• Dashboard renames repaint open-tab context immediately;
• dirty, conflict, deleted, and close indicators retain their established
  order and behavior.

The issue body and ADR-0003 now reflect the #471 decision that savedId already
provides stable query-tab identity; this PR deliberately adds no redundant
QueryTabOrigin state.

Validation

• npm test — pass; 100% statements/lines, 99.94% functions, 96.84% branches
• npm run build — pass; single dist/sql.html
• focused Playwright tab/variable suites — 82 passed, 2 skipped across Chromium, Firefox,
  and WebKit
• full Playwright run — 518 passed; five unrelated WebKit keyboard-focus
  failures reproduce on untouched base commit 3259b54
• driven Chromium — collision badges, focus ring, accessible tree, tooltips,
  close behavior, and badge disappearance verified

Checklist

• npm test passes (the per-file coverage gate is non-negotiable)
• Tests added/updated in the same change as the code
• npm run build succeeds (single-file dist/sql.html)
• Layers kept honest: pure logic in src/core/, network in src/net/ (injected fetch), DOM in src/ui/
• No new runtime dependency (or it's a deliberate, justified addition — see CONTRIBUTING)
• README / CHANGELOG.md ([Unreleased]) updated if behavior or the deployed surface changed
• Reconciled affected tracked work (roadmap Roadmap to 1.0.0 #68, the issue body, ADR/CHANGELOG) if this change reshaped it