fix(deepgram): use correct /v1/projects/{project_id}/keys endpoint

- Replace non-existent /v1/auth/grant with /v1/projects/{project_id}/keys
- Add DEEPGRAM_PROJECT_ID env variable
- Update request body and response parsing
- Update tests

Typecheck: OK · Tests: 241/241 ✅

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

.env.example

@@ -6,6 +6,7 @@ SUPABASE_SERVICE_ROLE_KEY=xxx
 DEEPSEEK_API_KEY=xxx
 GEMINI_API_KEY=xxx
 DEEPGRAM_API_KEY=xxx
+DEEPGRAM_PROJECT_ID=xxx
 
 # Stripe
 STRIPE_SECRET_KEY=xxx