fix: infra: deprecate tracked docker/Caddyfile — generate_caddyfile is the single source of truth (#771)

- Add docker/Caddyfile to .gitignore (generated artifact, not tracked)
- Document generate_caddyfile as canonical source in lib/generators.sh

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

.gitignore

@@ -33,6 +33,9 @@ docker/agents/bin/
 # Note: This file is now committed to track volume mount configuration
 # docker-compose.yml
 
+# Generated Caddyfile — single source of truth is generate_caddyfile in lib/generators.sh
+docker/Caddyfile
+
 # Python bytecode
 __pycache__/
 *.pyc