feat: add global search

[BeneficialVast1048]

Closes #3

Summary

Add an authenticated global search feature with a backend /api/v1/search/ endpoint scoped to each user's visible items, superuser user search by email/name, frontend service types, a /search page, and a sidebar Search entry.

Verification

• npm.cmd run build
• python -m compileall app
• Added focused backend pytest coverage for normal-user item scoping and superuser user results; local execution is blocked because this environment has no Postgres service on localhost:5432 and Docker is unavailable.

Happy to address any review feedback.

[BeneficialVast1048]

Update: I expanded this PR from UI-only filtering into an authenticated global search feature.

What changed:

• Added GET /api/v1/search/ for item search, scoped to the current user's visible items.
• Added superuser user search by email/full name.
• Added backend tests covering normal-user item scoping and superuser user results.
• Added frontend client types/service, a dedicated /search page, and a sidebar Search link.

Validation:

• npm.cmd run build passes.
• python -m compileall app passes.
• I also prepared the focused pytest coverage, but could not execute it in this local environment because the backend test database requires Postgres on localhost:5432 and Docker is not installed here.