Add image search with local cache (Phase 23)

Images found via SearXNG are fetched server-side, stored on disk, and
served from /api/images/<id> — the user's browser never contacts the
original image host.  Original URLs are preserved for citation.

New files:
- alembic/versions/0016_add_image_cache.py  — image_cache table
- src/fabledassistant/models/image_cache.py — SQLAlchemy model
- src/fabledassistant/services/images.py    — fetch/store/serve logic
- src/fabledassistant/routes/images.py      — GET /api/images/<id>

Modified:
- config.py: IMAGE_CACHE_DIR (/data/images), IMAGE_MAX_BYTES (5 MB)
- research.py: _search_searxng_images() — SearXNG categories=images
- tools.py: _IMAGE_TOOLS def + search_images branch in execute_tool
- intent.py: search_images routing rule (explicit visual language only)
- app.py: register images_bp
- docker-compose.yml: image_cache named volume mounted at /data/images
- ToolCallCard.vue: "image_search" label

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

src/fabledassistant/services/tools.py

@@ -710,6 +710,33 @@ _RESEARCH_TOOLS = [
     }
 ]
 
+_IMAGE_TOOLS = [
+    {
+        "type": "function",
+        "function": {
+            "name": "search_images",
+            "description": (
+                "Search the web for images and display them inline in the response. "
+                "ONLY use this when the user explicitly asks to SEE, SHOW, VIEW, or DISPLAY "
+                "an image or photo — e.g. 'show me a picture of X', 'what does X look like', "
+                "'find a photo of X', 'display an image of X'. "
+                "Do NOT use for general descriptions, factual questions, or when the user just "
+                "wants information without visual content. Returns at most 2 images."
+            ),
+            "parameters": {
+                "type": "object",
+                "properties": {
+                    "query": {
+                        "type": "string",
+                        "description": "The image search query",
+                    }
+                },
+                "required": ["query"],
+            },
+        },
+    }
+]
+
 
 async def get_tools_for_user(user_id: int) -> list[dict]:
     """Build the tool list for a user based on their configured integrations."""
@@ -719,6 +746,7 @@ async def get_tools_for_user(user_id: int) -> list[dict]:
     if Config.searxng_enabled():
         tools.extend(_SEARCH_TOOLS)
         tools.extend(_RESEARCH_TOOLS)
+        tools.extend(_IMAGE_TOOLS)
     logger.debug("User %d: %d tools available", user_id, len(tools))
     return tools
 
@@ -1215,6 +1243,41 @@ async def execute_tool(user_id: int, tool_name: str, arguments: dict) -> dict:
                 "data": {"topic": topic},
             }
 
+        elif tool_name == "search_images":
+            from fabledassistant.services.images import fetch_and_store_image
+            from fabledassistant.services.research import _search_searxng_images
+            query = arguments.get("query", "")
+            if not query:
+                return {"success": False, "error": "query is required"}
+            raw_results = await _search_searxng_images(query)
+            if not raw_results:
+                return {"success": False, "error": f"No images found for '{query}'"}
+            # Fetch and cache up to 2 images
+            images = []
+            for r in raw_results[:2]:
+                img_url = r.get("img_src", "")
+                if not img_url:
+                    continue
+                record = await fetch_and_store_image(
+                    url=img_url,
+                    title=r.get("title"),
+                    source_domain=r.get("source_domain"),
+                )
+                if record:
+                    images.append({
+                        "local_url": f"/api/images/{record.id}",
+                        "page_url": r.get("page_url", ""),
+                        "source_domain": r.get("source_domain", ""),
+                        "title": record.title or query,
+                    })
+            if not images:
+                return {"success": False, "error": f"Could not retrieve images for '{query}'"}
+            return {
+                "success": True,
+                "type": "image_search",
+                "data": {"query": query, "images": images},
+            }
+
         else:
             return {"success": False, "error": f"Unknown tool: {tool_name}"}