fix(file-search): claim owners woken by a file write ahead of backfill reconciliation - #9655

Summary

• The backfill walk wakes every owner a page passes so the dispatcher reconciles its builds. Those wake-ups entered the owner queue never dispatched, exactly like an owner the file trigger wakes for a write, and each claim pass takes never-dispatched owners first in enqueue order. A page across many small owners put dozens of wake-ups with nothing to claim ahead of a fresh upload, which then waited several passes (minutes) to be indexed. Owners with pending work that had been dispatched before waited behind every one of them, so a busy workspace could go an hour between turns.
• Backfill wake-ups now enter the queue as if just dispatched. Write-woken owners are claimed first; the wake-ups still rotate in by dispatch age, so reconciliation and backfill-found work are delayed behind fresh writes but never starved. An owner already queued keeps its place (the upsert is unchanged).
• Only the backfill enqueue changes. The release, reaper, and trigger paths still enqueue never-dispatched, per-owner (2) and global (100) caps are unchanged, no migration. README notes the ordering.

Type of Change

• Bug fix

Testing

• dispatcher.integration.ts (real PostgreSQL, bun run test:integration dispatcher.integration), three new tests:
  • a write-woken owner is claimed on the next pass behind a page of 250 reconciliation wake-ups — red on the old code (claimed nothing)
  • with one free slot per pass, a fresh write is claimed before work the backfill found, then the backfill work on the next pass — red on the old code (backfill work won, the write was not claimed in two passes)
  • an owner already queued by a write stays ahead of an owner served earlier when a backfill page passes it — red on a mutant whose upsert stamps existing rows
  • writes go through the real workspace_file_search_mark_pending trigger, not hand-written queue rows
• Whole suite 37/37; also ran owners.integration 18/18, chunks.integration 49/49 (1 opt-in skip), index-plan.integration 9/9, content-rendered.integration 31/31, dispatcher.test.ts + enqueue-dispatch.test.ts 17/17
• lint and type-check (pre-push hooks); remaining audits in CI

Checklist

• Code follows project style guidelines
• Self-reviewed my changes
• Tests added/updated and passing (new tests pass the test-audit authoring gate)
• No new warnings introduced
• I confirm that I have read and agree to the terms outlined in the Contributor License Agreement (CLA)