feat(config): split monolithic config + extract secrets

- Update .gitignore for v0.3 multi-file layout
- Add config/.env.example template for secrets
- Add config/local.yaml.example for operator values
- Wire main.py to use new config_loader
- Support both legacy and new layouts

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

.gitignore

@@ -1,3 +1,13 @@
+# Operator-identifying config and secrets (v0.3 split)
+/data/config/local.yaml
+/data/config/secrets/
+/data/secrets/
+.env
+.env.local
+.env.*
+!.env.example
+local.yaml
+!local.yaml.example
 # Python
 __pycache__/
 *.py[cod]
@@ -49,3 +59,13 @@ data/
 # OS
 .DS_Store
 Thumbs.db
+# Operator-identifying config and secrets (v0.3 split)
+/data/config/local.yaml
+/data/config/secrets/
+/data/secrets/
+.env
+.env.local
+.env.*
+!.env.example
+local.yaml
+!local.yaml.example