fix: WHIP/WHEP inactive status, CouchDB resilience, and CORS centralization

[LucasMaupin]

Summary

Fixes three related issues with WHIP/WHEP session management and CouchDB stability:

• WHIP/WHEP sessions never shown as inactive: All three API response mappings (api_productions.ts x2, production_manager.ts x1) forced isActive: true for WHIP sessions, so they'd jump straight from active to gone when expired. Now passes through the actual DB value.
• CouchDB crash loop (146+ restarts on intercomprod): Transient network errors (ECONNRESET, socket hang up) on CouchDB calls were unhandled, crashing the Node.js process. Adds withRetry() wrapper around ALL nano DB operations with exponential backoff, connection retry (5 attempts), and 10s request timeout.
• CORS centralization: Moves wildcard CORS from per-route onSend hooks in api_whip.ts/api_whep.ts to a centralized delegator in the @fastify/cors plugin. WHIP/WHEP routes get origin: '*', everything else uses CORS_ORIGIN.

Changes

src/db/couchdb.ts

• withRetry<T>() — generic retry wrapper for all DB operations (3 retries, 100/200/400ms backoff)
• isTransientError() — detects ECONNRESET, ETIMEDOUT, socket hang up, EHOSTUNREACH
• connect() — retry with backoff (5 attempts, 1/2/4/8/16s)
• nano client configured with 10s request timeout
• Proper 404 handling in getNextSequence (no longer swallows non-404 errors)

src/db/couchdb.test.ts

• 360 lines of new tests covering retry behavior, transient error handling, connection failures

src/server.ts

• process.exit(1) in uncaughtException handler for clean pod restart

src/api_productions.ts

• Lines 514, 948: isActive: s.isWhip ? true : ... → isActive: !!s.isActive

src/production_manager.ts

• Line 490: same isWhip override removed

src/api.ts

• Centralized CORS delegator: WHIP/WHEP routes get origin: '*', all other routes use CORS_ORIGIN

src/api_whip.ts / src/api_whep.ts

• Removed redundant per-route onSend CORS hooks

Test plan

• All 228 backend tests pass
• Start a WHIP session → verify it shows as active
• Stop the WHIP source → verify it transitions to "(inactive)" before disappearing
• Simulate CouchDB transient error → verify retry succeeds without process crash
• Verify WHIP/WHEP endpoints respond with Access-Control-Allow-Origin: *
• Verify non-WHIP/WHEP endpoints use restrictive CORS from CORS_ORIGIN
• Deploy to beta and confirm pod restart count stabilizes

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