Force dark mode site-wide and cap CT GPU duration

- Force ?__theme=dark via gr.Blocks js= so light-mode visitors get the
intended dark "MAISI Console" aesthetic instead of washed-out light tokens.
- Add <meta name="color-scheme" content="dark"> via head= so native browser
chrome paints dark before hydration.
- Reduce CT @spaces.GPU duration 300s -> 180s; 300s exceeded the ZeroGPU
maximum allowed (180s) and rejected CT generations upfront.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

app.py

@@ -44,7 +44,7 @@ _ensure_upstream()
 # ZeroGPU decorator — present on HF Spaces, optional locally.
 try:
     import spaces  # type: ignore
-    spaces_gpu_ct = spaces.GPU(duration=300)
+    spaces_gpu_ct = spaces.GPU(duration=180)
     spaces_gpu_mr = spaces.GPU(duration=180)
     spaces_gpu_mr_brain = spaces.GPU(duration=180)
 except (ImportError, AttributeError):
@@ -1425,8 +1425,25 @@ footer { display: none !important; }
 """
 
 
+FORCE_DARK_JS = """
+() => {
+  const url = new URL(window.location);
+  if (url.searchParams.get('__theme') !== 'dark') {
+    url.searchParams.set('__theme', 'dark');
+    window.location.replace(url.href);
+  }
+}
+"""
+
+FORCE_DARK_HEAD = '<meta name="color-scheme" content="dark">'
+
+
 def build_app() -> gr.Blocks:
-    with gr.Blocks(title="NV-Generate") as app:
+    with gr.Blocks(
+        title="NV-Generate",
+        js=FORCE_DARK_JS,
+        head=FORCE_DARK_HEAD,
+    ) as app:
         hero_group, hero_buttons = render_hero()
         ct_group, ct_back = workspace_ct.build(spaces_gpu_ct)
         mr_group, mr_back = workspace_mr.build(spaces_gpu_mr)