Add per-user sessions and memory filters in admin panel ...

Backend:
- GET /admin/memory now accepts user_id query param to filter facts
  for a specific user instead of returning the global view.

Frontend:
- Users table now has "Sessions" and "Memory" buttons per row.
- Clicking "Sessions" switches to Sessions tab and pre-fills search
  with the user id.
- Clicking "Memory" switches to Memory tab and passes user_id to the
  API, showing only that user's facts.
- Manual tab clicks reset filters (search / userId) so the view
  returns to unfiltered state.

Docs:
- docs/api.md updated with user_id param for GET /admin/memory.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

Fix admin memory showing 0 facts; add pagination/search/sort ...

Bug fix:
- get_all_facts(user_id=None) was filtering for user_id IS NULL only,
  so admin panel showed 0 facts when facts had user_ids set.
- Added all_users parameter to get_all_facts and fact_count.
- Admin endpoint now passes all_users=True to return all facts.

Memory pagination:
- Extended get_all_facts with offset, search, sort_by, sort_order params.
- Extended fact_count with search and all_users params.
- /admin/memory endpoint now accepts limit, offset, search, sort_by,
  sort_order and returns {total, limit, offset, items}.

Admin panel frontend:
- Added server-side search with debounce for memory facts.
- Added sortable column headers (category, key, source, confidence, updated).
- Added pagination controls (prev/next, page size selector).
- Switched memory display from grouped tables to flat sortable table.

Tests:
- Added unit tests for get_all_facts(all_users=True) and
  fact_count(all_users=True).
- All 219 tests pass.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

Add pagination, search, and sorting to admin sessions ...

Backend:
- Add count_all and search_list abstract methods to SessionStore
- Implement count_all and search_list in PgSessionStore (SQL with ILIKE)
- Implement count_all and search_list in InMemorySessionStore
- Update /admin/sessions to accept limit, offset, search, sort_by, sort_order
- Return {total, limit, offset, items} from /admin/sessions

Frontend:
- Add search input for sessions in admin panel
- Add clickable sortable column headers with asc/desc toggle
- Add pagination controls (prev/next, page size selector, item count)
- Debounce search input (300ms)

Tests:
- Add integration tests for pagination, offset, search, and sorting
- All 217 tests pass

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>