vscode: add Codev: Search Backlog... Quick Pick command (#918)

[amrmelsayed]

PIR Review: VSCode Quick Pick command for searching the backlog

Fixes #918

Summary

Adds a codev.searchBacklog command (palette title Codev: Search Backlog...)
that opens a VSCode Quick Pick over the current open backlog with built-in fuzzy
match on issue id, title, area, and assignee. Selecting a row opens the issue via
the same codev.viewBacklogIssue flow a single sidebar-row click uses. This gives
the Backlog tree the find-by-recall / find-by-topic affordance it lacked — without
a webview (#906's path) or the impossible in-tree <input> (closed in pir-891).

Files Changed

• packages/vscode/src/views/backlog-search.ts (+82 / -0) — new, vscode-free: orderForSearch + toQuickPickItems
• packages/vscode/src/commands/search-backlog.ts (+36 / -0) — new: command handler
• packages/vscode/src/__tests__/backlog-search.test.ts (+97 / -0) — new: 7 unit tests
• packages/vscode/src/extension.ts (+2 / -0) — register codev.searchBacklog
• packages/vscode/package.json (+5 / -0) — command contribution

Commits

• 65bb678d [PIR vscode: Quick Pick command for searching the backlog #918] Add Codev: Search Backlog... Quick Pick command
• fa8ee2c7 [PIR vscode: Quick Pick command for searching the backlog #918] Update builder thread (implement phase)

Test Results

• pnpm check-types: ✓ pass
• pnpm lint: ✓ pass (clean)
• pnpm test:unit (vitest): ✓ pass (120 tests, 7 new in backlog-search.test.ts)
• Porch checks: build ✓ (5.9s), tests ✓ (20.6s)
• Manual verification: approved by the human at the dev-approval gate via the
  Extension Development Host — command appears in the palette, picker lists open
  backlog issues, fuzzy filtering and selection-opens-issue verified.

Architecture Updates

No arch changes — this PR adds a self-contained command that reuses the existing
OverviewCache data source and the existing codev.viewBacklogIssue action. It
introduces no new module boundary or pattern; the pure-helper-in-a-vscode-free-file
split it follows is the already-documented backlog-filter.ts convention.

Lessons Learned Updates

No lessons captured — the change applied established conventions (vscode-free pure
helpers unit-tested from __tests__/, command registration in extension.ts,
palette visibility via the absence of a commandPalette when:false suppressor)
with no surprises worth recording for future work.

Things to Look At During PR Review

• detail deliberately omitted. The issue floated an optional detail =
  issue-body first sentence. OverviewBacklogItem carries no body field, and
  fetching one would add the data path the issue explicitly forbids ("snapshot
  from overviewCache … no new data path"). So detail is not set. matchOnDetail: true is still passed — harmless today, and correct if a detail is added later.
• orderForSearch is intentionally NOT BacklogProvider.orderedSpawnable.
  The tree's helper applies the mine-only filter; search must run over the full
  backlog (issue decision 1). orderForSearch reuses spawnableBacklog and the
  mine-first segment split but skips the mine-only filter. BacklogProvider is
  left untouched (it could later delegate its split to the shared helper — out of
  scope here).
• now injection in toQuickPickItems is purely for deterministic relative-age
  tests; the command passes Date.now().

How to Test Locally

For reviewers pulling the branch:

• View diff: VSCode sidebar → right-click builder pir-918 → View Diff
• Run it: this is a VSCode extension surface — launch the Extension
  Development Host (F5 in packages/vscode), not afx dev (which runs
  Tower/dashboard, a different surface).
• What to verify (maps to the plan's Test Plan):
  • Codev: Search Backlog... appears in the Command Palette.
  • Invoking it opens a Quick Pick listing every open spawnable backlog issue.
  • Typing an id / title fragment / area / assignee fuzzy-filters the list.
  • Selecting a row opens the same markdown preview a single sidebar click does.
  • Esc / click-away dismisses with no side effect.
  • Works with the Backlog sidebar view collapsed or hidden.