feat(search): add offset pagination to GLOBAL_SEARCH

[pedrofrxncx]

Source: hardening gap in the GLOBAL_SEARCH tool (apps/api/src/tools/search/global-search.ts) — the tool hardcoded offset: 0 on every call, so a caller with more than limit (max 50) matching threads in an org could never reach results past the first page.

Why: COLLECTION_THREADS_LIST already exposes offset/hasMore for the exact same underlying threads.list() storage call — GLOBAL_SEARCH was missing the same pagination contract other list-style tools already follow, so a caller has no way to page through search results for orgs with lots of matching threads.

What changed: added an optional offset field to the input schema (int, min 0, default 0) that's threaded through to ctx.storage.threads.list(), and an hasMore boolean to the output schema (offset + limit < total), mirroring COLLECTION_THREADS_LIST's existing pagination shape. Both fields are additive/optional, so existing callers (the global-search dialog in the web UI) are unaffected.

Verification:

• bun run fmt
• cd apps/api && bunx tsc --noEmit — clean
• bun test apps/api/src/tools/search/global-search.test.ts — 4/4 pass (added two cases: negative offset rejected, offset omitted defaults to undefined)

A reviewer can confirm with the same targeted test command above. Full CI validates the DB-backed integration test (global-search.integration.test.ts), which needs Postgres and wasn't runnable locally in this environment.

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Summary by cubic

Add offset-based pagination to GLOBAL_SEARCH so callers can page through results and see if more pages exist. Removes the hardcoded offset: 0 that hid results beyond the first page.

• New Features
  • Input: optional offset (int ≥ 0, default 0) passed to ctx.storage.threads.list().
  • Output: hasMore boolean computed as offset + limit < total.
  • Pagination shape matches COLLECTION_THREADS_LIST; existing callers continue working with defaults.

^{Written for commit 15a6aca. Summary will update on new commits.}