Add image upload and vision analysis to Ask Simba chat

Users can now attach images in the web chat for Simba to analyze using
Ollama's gemma3 vision model. Images are stored in Garage (S3-compatible)
and displayed in chat history.

Also fixes aerich migration config by extracting TORTOISE_CONFIG into a
standalone config/db.py module, removing the stale aerich_config.py, and
adding missing MODELS_STATE to migration 3.

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

config/db.py

@@ -0,0 +1,23 @@
+import os
+
+from dotenv import load_dotenv
+
+load_dotenv()
+
+DATABASE_URL = os.getenv(
+    "DATABASE_URL", "postgres://raggr:raggr_dev_password@localhost:5432/raggr"
+)
+
+TORTOISE_CONFIG = {
+    "connections": {"default": DATABASE_URL},
+    "apps": {
+        "models": {
+            "models": [
+                "blueprints.conversation.models",
+                "blueprints.users.models",
+                "aerich.models",
+            ],
+            "default_connection": "default",
+        },
+    },
+}