Rebuild: settling quiet releases

Hourly in coordinator:run: a release unchanged for 6 hours is settled,
complete when every file its [i/N] counter announced was found, unknown
without a counter (phase 2 reads par2 sets for those). Partial index on
unsettled releases.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

database/migrations/1770000001000_releases_unsettled_index.ts

@@ -0,0 +1,12 @@
+import { BaseSchema } from '@adonisjs/lucid/schema'
+
+/** Releases still to settle (REBUILD.md, part 8), by when they last changed. */
+export default class extends BaseSchema {
+  async up() {
+    this.schema.raw(`CREATE INDEX IF NOT EXISTS releases_unsettled_idx ON releases (last_seen_at) WHERE settled_at IS NULL`)
+  }
+
+  async down() {
+    this.schema.raw(`DROP INDEX IF EXISTS releases_unsettled_idx`)
+  }
+}