Implement global search

[raulvbrito]

Summary

• Add an authenticated /api/v1/search/ endpoint for records the current user can access
• Search items for normal users, and search both items and users for superusers
• Add a reusable sidebar global search UI with result navigation
• Add focused backend route tests and update the generated frontend client types/service

Validation

• npm run build
• .venv/bin/python -m compileall app/api/routes/search.py app/models.py app/api/main.py
• .venv/bin/ruff check app/api/routes/search.py app/api/main.py app/models.py app/tests/api/routes/test_search.py

Notes

• I attempted pytest app/tests/api/routes/test_search.py -q, but the local checkout expects PostgreSQL at localhost:5432 with role postgres and database gitearn; that role does not exist on this machine, so test setup fails before the new tests execute.

Closes #3
/claim #3