Fix stale UI cache, BEN2 edge quality, and fresh-install permissions

- Serve /dist and /src with Cache-Control: no-cache so browsers always
  revalidate the webpack bundle (it has a fixed filename with no content
  hash, so a stale browser cache was hiding the new Remove Background
  model dropdown after the rebuild).
- Enable BEN2's refine_foreground pass by default - it's the model's own
  documented option for preserving fine/semi-transparent edge detail
  (text borders, light rays) instead of a harder cutout, at a small
  speed cost.
- Make install-local-gpu.sh and bring-up-local-gpu.sh pre-create ./data
  as the invoking non-root user before Docker ever runs, so its daemon
  never gets a chance to auto-create those bind-mount dirs as root.
- Make prefetch-models.sh self-heal a root-owned ./data automatically
  (sudo chown) instead of erroring out with a manual fix-it command.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01Ro4PwQKvSc3CH19LSN21Ht

backend/app/main.py

@@ -103,20 +103,31 @@ def health():
 STATIC_DIR = Path("/app/static")
 
 
+class NoCacheStaticFiles(StaticFiles):
+    """webpack outputs a fixed 'bundle.js' filename (no content hash), so
+    browsers can keep serving a stale cached copy after a rebuild unless
+    forced to revalidate on every request."""
+
+    def file_response(self, *args, **kwargs):
+        response = super().file_response(*args, **kwargs)
+        response.headers["Cache-Control"] = "no-cache"
+        return response
+
+
 # Serve static assets - mount subdirectories if they exist
 if STATIC_DIR.exists():
     # React-style assets folder
     if (STATIC_DIR / "assets").exists():
         app.mount("/assets", StaticFiles(directory=STATIC_DIR / "assets"), name="assets")
-    # miniPaint dist folder (webpack bundle)
+    # miniPaint dist folder (webpack bundle) - no-cache so code updates are picked up immediately
     if (STATIC_DIR / "dist").exists():
-        app.mount("/dist", StaticFiles(directory=STATIC_DIR / "dist"), name="dist")
+        app.mount("/dist", NoCacheStaticFiles(directory=STATIC_DIR / "dist"), name="dist")
     # miniPaint images folder
     if (STATIC_DIR / "images").exists():
         app.mount("/images", StaticFiles(directory=STATIC_DIR / "images"), name="images")
-    # miniPaint CSS folder
+    # miniPaint CSS folder - no-cache, same reasoning as /dist
     if (STATIC_DIR / "src").exists():
-        app.mount("/src", StaticFiles(directory=STATIC_DIR / "src"), name="src")
+        app.mount("/src", NoCacheStaticFiles(directory=STATIC_DIR / "src"), name="src")
 
 
 @app.get("/", response_class=HTMLResponse)
@@ -124,7 +135,7 @@ async def serve_spa():
     """Serve miniPaint index.html"""
     index_path = STATIC_DIR / "index.html"
     if index_path.exists():
-        return FileResponse(index_path)
+        return FileResponse(index_path, headers={"Cache-Control": "no-cache"})
     return HTMLResponse("<h1>Frontend not built. Run npm build in frontend/</h1>")
 
 
@@ -146,6 +157,6 @@ async def serve_spa_routes(request: Request, full_path: str):
     # Otherwise serve index.html
     index_path = STATIC_DIR / "index.html"
     if index_path.exists():
-        return FileResponse(index_path)
+        return FileResponse(index_path, headers={"Cache-Control": "no-cache"})
 
     return HTMLResponse("<h1>Frontend not built</h1>", status_code=404)

backend/app/routers/tools.py

@@ -369,7 +369,10 @@ async def _remove_background_ben2(img: Image.Image) -> bytes:
         _ben2_model.to(device).eval()
         print("BEN2_Base model loaded")
 
-    result = _ben2_model.inference(img.convert('RGB'), refine_foreground=False)
+    # refine_foreground=True runs BEN2's extra foreground-color refinement pass
+    # (slower, but recovers fine/semi-transparent edge detail instead of a hard
+    # cutout — matters for things like lace, light rays, or fine text borders).
+    result = _ben2_model.inference(img.convert('RGB'), refine_foreground=True)
 
     buffer = BytesIO()
     result.save(buffer, format='PNG')