ci: add proto validation step to catch API contract drift

Added a CI step that:
- Refreshes Node fixtures from the staging container after deployment
- Runs tools/validate-protos.py to validate proto definitions match actual API responses
- Fails the pipeline if proto drift is detected

This ensures nobody can merge a Node change that breaks the Go proto contract
without updating the .proto definitions.

The step runs after the Node staging healthcheck, capturing fresh responses
from 19 API endpoints (stats, health, nodes, analytics/*, config/*, etc.).
Endpoints requiring parameters (node-detail, packet-detail) use existing
fixtures and aren't auto-refreshed.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

.github/workflows/deploy.yml

@@ -364,6 +364,42 @@ jobs:
           curl -f http://localhost:81/api/nodes || exit 1
           echo "Node staging smoke tests passed ✅"
 
+      - name: Validate API contract (proto vs Node fixtures)
+        run: |
+          set -e
+          echo "Refreshing Node fixtures from staging container..."
+          mkdir -p proto/testdata/node-fixtures
+          
+          # Capture fresh API responses from staging container
+          # Only refresh endpoints that don't require parameters
+          ENDPOINTS=(
+            "stats" "health" "perf" "nodes" "packets" "observers" "channels"
+            "analytics/rf" "analytics/topology" "analytics/channels"
+            "analytics/hash-sizes" "analytics/distance" "analytics/subpaths"
+            "config/theme" "config/regions" "config/client" "config/cache" "config/map"
+            "iata-coords"
+          )
+          
+          for endpoint in "${ENDPOINTS[@]}"; do
+            # Convert /api/analytics/rf → analytics-rf.json
+            fixture_name=$(echo "$endpoint" | tr '/' '-')
+            echo "  Fetching $endpoint → ${fixture_name}.json"
+            docker exec meshcore-staging wget -qO- "http://localhost:3000/api/$endpoint" \
+              > "proto/testdata/node-fixtures/${fixture_name}.json" 2>/dev/null || {
+                echo "  ⚠ Failed to fetch $endpoint (container may not have data yet)"
+              }
+          done
+          
+          echo ""
+          echo "Running proto validator..."
+          python3 tools/validate-protos.py || {
+            echo "❌ Proto validation failed — API contract drift detected"
+            echo "This means a Node.js API response doesn't match the proto definition."
+            echo "Fix by updating the .proto files in proto/ to match the actual API responses."
+            exit 1
+          }
+          echo "✅ Proto validation passed — API contract is consistent"
+
   # ───────────────────────────────────────────────────────────────
   # 6. Deploy Go Staging — start on port 82, healthcheck, smoke test
   # ───────────────────────────────────────────────────────────────