chore: dockerize api proxy and add gitignore

Add a Docker-based FastAPI proxy skeleton (charter §4) for parity across
dev / homelab VPS / fly.io, plus root .gitignore for Godot 4.7 and Python.

- api/Dockerfile: python:3.12-slim, non-root, PORT-aware CMD
- api/app/main.py: /health + five role endpoint stubs (§4)
- api/requirements.txt: fastapi/uvicorn/httpx/pydantic, pinned
- docker-compose.yml: local dev with live reload
- api/fly.toml: prod deploy stub with /health check
- api/.env.example: key lives in the proxy, never the client (§4)
- .gitignore: ignores .env, whitelists .env.example

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

api/.env.example

@@ -0,0 +1,11 @@
+# Copy to .env for local dev. NEVER commit the real .env. The client never sees
+# any of these — keys live only in the proxy (charter §4).
+
+# Where the proxy sends model calls in dev (Ollama on the homelab).
+OLLAMA_BASE_URL=http://localhost:11434
+
+# Prod model provider (charter §4). Leave blank in dev.
+REPLICATE_API_TOKEN=
+
+# Port the proxy binds. compose / fly.io override this.
+PORT=8000