fix(theme): remove every hardcoded Apple/Material colour left in the UI

Porting the palette was not enough: the Warm Cinema charter only reached the
widgets that read from AppColors. Nineteen screen and widget files still painted
Apple TV values inline, so the app kept showing blue — most visibly on the
selected navigation pill.

Swept out:
- 0xFF0A84FF (Apple blue) on the selected nav pill, category card icons and the
  "add playlist" button
- 0xFF4FC3F7 and 0xFF1565C0 in the player overlays
- Colors.blueAccent / Colors.blue in dialogs
- Apple greys 1C1C1E / 2C2C2E / 3A3A3C / 8E8E93 -> warm charcoals
- 128 Colors.white* -> the onSurfaceNN cream ladder (a pure white on a warm
  ground reads blue, which is the charter's whole point)
- Colors.red / green / amber / yellow / grey* -> error, success, ratingGold,
  outlineVariant
- pure black ink on light fills -> onPrimaryFixed, a warm near-black
- the white focus glow -> an ember glow

Deliberately left true black: the video surface backgrounds and the scrims over
posters and video, where a warm tint would clash with the picture.

Adds the onPrimaryFixed / primaryFixed / onSurface70 tokens the sweep needed.

Verified: no Material or Apple colour literal remains outside lib/core/theme;
flutter analyze reports no errors; 19/19 tests pass; release APK builds.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

lib/core/widgets/themed_loading_screen.dart

@@ -1,4 +1,5 @@
 import 'package:flutter/material.dart';
+import 'package:xtremobile/core/theme/app_colors.dart';
 
 class ThemedLoading extends StatelessWidget {
   const ThemedLoading({super.key});
@@ -11,7 +12,7 @@ class ThemedLoading extends StatelessWidget {
           center: Alignment(0, -0.2),
           radius: 1.5,
           colors: [
-            Color(0xFF2C2C2E),
+            AppColors.surfaceContainerHigh,
             Color(0xFF000000),
           ],
           stops: [0.0, 1.0],
@@ -19,7 +20,7 @@ class ThemedLoading extends StatelessWidget {
       ),
       child: const Center(
         child: CircularProgressIndicator(
-          color: Colors.white,
+          color: AppColors.onSurface,
           strokeWidth: 3,
         ),
       ),