perf(web): cache macro images in local PWA, bump to 1.1.2

Same fix as the relay: the local PWA re-fetched every macro image and revoked
the blob on each re-render. Cache image URL -> Promise<objectURL> and reuse
across renders (images are immutable per uuid path); add Cache-Control:
immutable on the desktop /api/image response. Verified in a browser: 7
re-renders produced only the initial 3 image fetches, none repeated.

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

web_server.py

@@ -338,7 +338,11 @@ class WebServer:
             # Only serve files that resolve to inside the macro_images directory
             if (os.path.commonpath([requested, images_real]) == images_real
                     and os.path.isfile(requested)):
-                return FileResponse(requested)
+                # Macro images are content-addressed (uuid filenames) and thus
+                # immutable, so let the browser cache them aggressively.
+                return FileResponse(requested, headers={
+                    "Cache-Control": "private, max-age=31536000, immutable"
+                })
             raise HTTPException(status_code=404, detail="Image not found")
 
         @app.websocket("/ws")