feat(api): add debug endpoints for prod/local diagnosis

[GMNAPI]

Summary

Adds comprehensive debug endpoints to diagnose why production returns low-confidence responses while local environment works correctly (issue #16).

What's Added

New Endpoint: GET /debug
Returns complete diagnostic information:

• Version info (git commit SHA, build time, Node version)
• Configuration (models, temperature, thresholds)
• Vector store stats (mode, document count)
• Sample embeddings (first 5 values from 2 chunks)
• Environment info (API key prefix, platform)

Enhanced Endpoint: POST /retrieve
Now includes:

• queryEmbedding: First 10 values for comparison
• embeddingPrefix: First 10 values for each retrieved chunk

How to Use

Test Locally:

# Start server
pnpm dev

# Test debug endpoint
curl http://localhost:3000/debug | jq '.'

# Test retrieve with embeddings
curl -X POST http://localhost:3000/retrieve \
  -H "Content-Type: application/json" \
  -d '{"question":"Qué es el Bono Alquiler Joven?"}' | jq '.'

Compare Local vs Prod:

# Use helper script (in temp/ folder, not committed)
chmod +x temp/helperScript_testDebugEndpoints.sh
./temp/helperScript_testDebugEndpoints.sh

# Review outputs
cat temp/debug_local.json
cat temp/debug_prod.json

Diagnosis Steps (Next)

1. ✅ Deploy this PR to production
2. Run diagnostic script to compare:
   • Git commit SHAs (must match)
   • Sample embeddings (if different → embeddings issue)
   • Query embeddings (consistency check)
3. Identify root cause:
   • Embeddings differ: Re-ingest vector store in prod
   • Embeddings match: Improve prompt robustness or change model

Related

• Issue 🔍 Prod vs Local Inconsistency - Diagnosis #16: Investigation tracking
• PR feat(rag): Actionable fallback with clickable sources #15: Actionable fallback (works locally, not in prod)

Test plan

• Debug endpoint returns expected structure
• Retrieve endpoint includes embedding prefixes
• Deploy to Railway and test /debug endpoint
• Compare local vs prod embeddings
• Identify root cause based on comparison

🤖 Generated with Claude Code