refactor: replace vision stub with cf-vision shim (cf-core#36)

circuitforge_core.vision.router now re-exports VisionRouter from the
standalone cf-vision repo. Existing imports unchanged; falls back to
a helpful ImportError stub if cf-vision is not installed.

Closes cf-core#36

circuitforge_core/vision/router.py

@@ -1,19 +1,26 @@
-"""
-Vision model router — stub until v0.2.
-Supports: moondream2 (local) and Claude vision API (cloud).
-"""
+# circuitforge_core/vision/router.py — shim
+#
+# The vision module has been extracted to the standalone cf-vision repo.
+# This shim re-exports VisionRouter so existing imports continue to work.
+# New code should import directly from cf_vision:
+#
+#   from cf_vision.router import VisionRouter
+#   from cf_vision.models import ImageFrame
+#
+# Install: pip install -e ../cf-vision
 from __future__ import annotations
 
+try:
+    from cf_vision.router import VisionRouter  # noqa: F401
+    from cf_vision.models import ImageFrame    # noqa: F401
+except ImportError:
+    # cf-vision not installed — fall back to the stub so products that don't
+    # need vision yet don't hard-fail on import.
+    class VisionRouter:  # type: ignore[no-redef]
+        """Stub — install cf-vision: pip install -e ../cf-vision"""
 
-class VisionRouter:
-    """Routes image analysis requests to local or cloud vision models."""
-
-    def analyze(self, image_bytes: bytes, prompt: str) -> str:
-        """
-        Analyze image_bytes with the given prompt.
-        Raises NotImplementedError until vision backends are wired up.
-        """
-        raise NotImplementedError(
-            "VisionRouter is not yet implemented. "
-            "Photo analysis requires a Paid tier or local vision model (v0.2+)."
+        def analyze(self, image_bytes: bytes, prompt: str = "", task: str = "document"):
+            raise ImportError(
+                "cf-vision is not installed. "
+                "Run: pip install -e ../cf-vision"
             )