refactor(#429): remove obsolete repair planner (phase 6)

[BorisTyshkevich]

What & why

Part of #429
Closes #500

Phase 6 records the final remove planner decision from #500. The unused
saved-query repair planner and its dedicated tests are deleted now that #494's
ownership-safe Panel and Dashboard trash actions are the supported cascading
delete paths. Library deletion and saved-query edits continue to use strict
whole-workspace validation and fail atomically rather than guessing repairs.

Replacement production-path coverage proves that:

• ownership on a non-current Dashboard excludes the query from Library and its
  trash controls;
• an ordinary zero-owner Library query still deletes and reconciles its linked
  tab while preserving every Dashboard;
• deleting or invalidating a query owned only by a non-current Dashboard is
  rejected with state byte-identical; and
• the retired planner API and repair vocabulary cannot be reintroduced into
  source or tests unnoticed.

Acceptance claimed from #429: the repair-planner disposition only. The
#438-gated Open-in-Dashboard focus work remains outside this phase.

Verification

• npm test — 183 files / 6,089 tests; TypeScript clean; 100% statements and
  lines
• npm run build — dist/sql.html built successfully
• npm run test:e2e -- --project=chromium --project=webkit --workers=1 —
  341 passed, 1 skipped
• sabotage check — forcing saved-query writes to ignore committed latest
  makes all three non-current-Dashboard safety tests fail
• two independent read-only reviews — clean after the whole-collection test
  finding was addressed

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
• README / CHANGELOG.md ([Unreleased]) updated if behavior or the deployed surface changed
• Reconciled affected tracked work: Dashboard tree management: direct Dashboard and Panel actions #429 phase contract/checklist and ship log; Remove obsolete saved-query repair planner and retire #429 repair phase #500 closes with this PR