Feature/saved searches

[HereIsMuhammad]

Closes #166

Summary

Adds saved developer searches with opt-in, per-search new-match alerts.

Signed-in users can save a search using a free-text query and/or structured filters such as country, language, and minimum score. They can re-run, rename, or delete saved searches.

See docs/prd/saved-searches.md for the full spec and API contract.

What's included

• lib/saved-search.js — criteria validation/normalization, structured + text filtering, privacy guard, and incremental deduplicated new-match detection (diffNewMatches)
• lib/saved-search-store.js — Cosmos-backed CRUD store with in-memory fallback, following lib/watchlist-store.js conventions
• lib/saved-search-run.js — executes saved searches using text/vector/hybrid mode against live data, reusing /api/search's existing Cosmos/embedding patterns
• GET/POST /api/saved-searches — list and create
• PATCH/DELETE /api/saved-searches/[id] — rename, update alert frequency, delete
• POST /api/saved-searches/[id]/run — run now, return results + deduplicated new matches, and update the persisted seen-set
• tests/saved-search.test.js — 21 tests covering validation, structured/text filtering, privacy exclusion, and incremental dedup

Acceptance criteria covered

• Save, rename, run, and delete search criteria
• Support current text/vector mode and structured filters
• New-match detection is incremental and deduplicated
• Alerts are opt-in with per-search frequency controls
• Private or pending profiles never appear

Out of scope

• Alert delivery (scheduled job + email/notification on the daily/weekly cadence). This PR ships the opt-in setting and dedup primitive; a future job will handle delivery.
• Saved Searches UI (save button, management screen) — API contract first, UI as a follow-up

Testing

node --test tests/saved-search.test.js — 21/21 passing, covering validation, structured/text filtering, privacy exclusion, and incremental dedup.

API routes follow the same auth/Cosmos/fallback pattern used by lib/watchlist-store.js and lib/feed-store.js.

The GitHub OAuth flow was not verified locally because it requires a separately configured OAuth app. Happy to have this checked on a deploy preview if useful.

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