fix(admin): speed up request model search

[mylukin]

Summary

• add a generated model_search column for admin request model/lane keyword filtering
• add SQLite/Postgres admin-window indexes so model= scans small indexed text instead of per-row decision_json paths
• bump version to 0.25.12 and document the performance decision

Live diagnosis

• reproduced /admin/api/requests?page=1&pageSize=50&model=fable&key_id=9ed9480f-519b-4350-85d5-3640a7071e5f&start=1783180800000&end=1783267200000
• before fix: TTFB ~5.26s, total ~5.65s
• production SQLite narrowed to 7,922 rows via key/date index, but COUNT still spent ~2.36s parsing JSON paths for model search

Verification

• pnpm exec vitest run packages/core/src/store/sqlite/schema.test.ts
• pnpm exec vitest run packages/core/src/store/postgres/migrate.test.ts
• pnpm exec vitest run packages/core/src/store/sqlite/telemetry.test.ts packages/core/src/store/store-contract.test.ts
• pnpm exec vitest run packages/core/src/store/sqlite/memory-dedup-migrate.test.ts packages/core/src/store/sqlite/memory-schema.test.ts packages/core/src/store/sqlite/oauth-quota-migrate.test.ts packages/core/src/store/sqlite/oauth-usage-migrate.test.ts
• pnpm test -> 5196 passed
• pnpm typecheck
• pnpm lint
• pnpm build