feat(cache): priority-based eviction with age protection and Bélády approximation

Replace the flat circular buffer with NodeAwareCache, a smarter eviction
strategy for historical mesh packet data:

- Packets younger than 1 hour are never evicted (recent traffic preserved)
- Under pressure, evict from the lowest-priority type first (neighbor-info
  outlasts node-info; chat messages outlast everything)
- Within a priority tier, evict from the most recently active source node —
  that node will resend soonest, so its old packet is cheapest to lose
  (Bélády approximation; protects flaky/distant node history)
- Node retention window still applies: silent nodes' packets are excluded
  from GetAll and pruned proactively before priority eviction runs

Also:
- Add --cache-retention flag (default 3h) and raise --cache-size default to 5000
- Fix decoder error strings (replace verbose Go errors with short codes)
- Add HTTP security headers middleware to server
- Fix broker dispatchLoop deadlock on source channel close
- Fix make gen-proto scanning web/node_modules for .proto files
- Fix tools target always reinstalling protoc-gen-go (handles stale arch binary)
- Move server port from 8080 to 5446; update Dockerfile, docker-compose, moat.yaml

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

.env.example

@@ -16,7 +16,7 @@ MESHSTREAM_SITE_DESCRIPTION=Development instance - Meshtastic activity in Bay Ar
 
 # For local development, point to local server 
 # (empty for production where API is on same domain)
-MESHSTREAM_API_BASE_URL=http://localhost:8080
+MESHSTREAM_API_BASE_URL=http://localhost:5446
 
 # Google Maps API configuration - required for maps to work
 # Get keys at: https://developers.google.com/maps/documentation/javascript/get-api-key
@@ -36,7 +36,7 @@ MESHSTREAM_MQTT_TOPIC_PREFIX=msh/US/bayarea
 
 # Server configuration
 MESHSTREAM_SERVER_HOST=0.0.0.0  # Listen on all interfaces
-MESHSTREAM_SERVER_PORT=8080     # Standard web port
+MESHSTREAM_SERVER_PORT=5446     # Standard web port
 MESHSTREAM_STATIC_DIR=/app/static
 
 # Logging and debugging