feat: band NC folder config, fix watcher event filter, add light/dark theme

- Add PATCH /bands/{id} endpoint for admins to update nc_folder_path
- Add band NC scan folder UI panel with inline edit
- Fix watcher: use activity type field (not human-readable subject) for upload detection
- Reorder watcher filters: audio extension check first, then band path, then type
- Add dark/light theme toggle using GitHub Primer-inspired CSS custom properties
- All inline styles migrated to CSS variables for theme-awareness

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

web/src/App.tsx

@@ -1,5 +1,7 @@
 import { QueryClient, QueryClientProvider } from "@tanstack/react-query";
 import { BrowserRouter, Route, Routes, Navigate } from "react-router-dom";
+import "./index.css";
+import { ThemeProvider, useTheme } from "./theme";
 import { LoginPage } from "./pages/LoginPage";
 import { HomePage } from "./pages/HomePage";
 import { BandPage } from "./pages/BandPage";
@@ -16,40 +18,73 @@ function PrivateRoute({ children }: { children: React.ReactNode }) {
   return token ? <>{children}</> : <Navigate to="/login" replace />;
 }
 
-export default function App() {
+function ThemeToggle() {
+  const { theme, toggle } = useTheme();
   return (
-    <QueryClientProvider client={queryClient}>
-      <BrowserRouter>
-        <Routes>
-          <Route path="/login" element={<LoginPage />} />
-          <Route
-            path="/bands/:bandId"
-            element={
-              <PrivateRoute>
-                <BandPage />
-              </PrivateRoute>
-            }
-          />
-          <Route
-            path="/bands/:bandId/songs/:songId"
-            element={
-              <PrivateRoute>
-                <SongPage />
-              </PrivateRoute>
-            }
-          />
-          <Route
-            path="/settings"
-            element={
-              <PrivateRoute>
-                <SettingsPage />
-              </PrivateRoute>
-            }
-          />
-          <Route path="/invite/:token" element={<InvitePage />} />
-          <Route path="/" element={<PrivateRoute><HomePage /></PrivateRoute>} />
-        </Routes>
-      </BrowserRouter>
-    </QueryClientProvider>
+    <button
+      onClick={toggle}
+      title={`Switch to ${theme === "dark" ? "light" : "dark"} mode`}
+      style={{
+        position: "fixed",
+        bottom: 20,
+        right: 20,
+        zIndex: 9999,
+        background: "var(--bg-subtle)",
+        border: "1px solid var(--border)",
+        borderRadius: "50%",
+        width: 36,
+        height: 36,
+        cursor: "pointer",
+        fontSize: 16,
+        display: "flex",
+        alignItems: "center",
+        justifyContent: "center",
+        color: "var(--text-muted)",
+        boxShadow: "0 2px 8px rgba(0,0,0,0.3)",
+      }}
+    >
+      {theme === "dark" ? "☀" : "◑"}
+    </button>
+  );
+}
+
+export default function App() {
+  return (
+    <ThemeProvider>
+      <QueryClientProvider client={queryClient}>
+        <BrowserRouter>
+          <Routes>
+            <Route path="/login" element={<LoginPage />} />
+            <Route
+              path="/bands/:bandId"
+              element={
+                <PrivateRoute>
+                  <BandPage />
+                </PrivateRoute>
+              }
+            />
+            <Route
+              path="/bands/:bandId/songs/:songId"
+              element={
+                <PrivateRoute>
+                  <SongPage />
+                </PrivateRoute>
+              }
+            />
+            <Route
+              path="/settings"
+              element={
+                <PrivateRoute>
+                  <SettingsPage />
+                </PrivateRoute>
+              }
+            />
+            <Route path="/invite/:token" element={<InvitePage />} />
+            <Route path="/" element={<PrivateRoute><HomePage /></PrivateRoute>} />
+          </Routes>
+          <ThemeToggle />
+        </BrowserRouter>
+      </QueryClientProvider>
+    </ThemeProvider>
   );
 }