fix(infra): harden AI service — graceful shutdown, rate limiting, API key auth, pinned deps, Grafana secrets

- Add dumb-init + --timeout-graceful-shutdown 30 to AI service Dockerfile
- Add slowapi rate limiting (configurable via AI_RATE_LIMIT) and X-API-Key auth middleware
- Pin all Python dependencies to exact versions for reproducible builds
- Move Grafana admin credentials from env vars to Docker secrets in production compose

Co-Authored-By: Paperclip <noreply@paperclip.ing>

libs/ai-services/pyproject.toml

@@ -4,14 +4,15 @@ version = "0.1.0"
 description = "AI/ML services for Goodgo Platform — AVM, feature extraction, moderation"
 requires-python = ">=3.12"
 dependencies = [
-    "fastapi>=0.115.0",
-    "uvicorn[standard]>=0.32.0",
-    "xgboost>=2.1.0",
-    "numpy>=1.26.0",
-    "underthesea>=6.8.0",
-    "pydantic>=2.9.0",
-    "pydantic-settings>=2.5.0",
-    "httpx>=0.27.0",
+    "fastapi==0.115.0",
+    "uvicorn[standard]==0.32.0",
+    "xgboost==2.1.0",
+    "numpy==1.26.4",
+    "underthesea==6.8.0",
+    "pydantic==2.9.0",
+    "pydantic-settings==2.5.0",
+    "httpx==0.27.0",
+    "slowapi==0.1.9",
 ]
 
 [project.optional-dependencies]