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/theme/app_colors.dart

@@ -53,6 +53,14 @@ class AppColors {
   /// en restant la même couleur perçue.
   static const Color primaryFill = Color(0xFFA8360C);
 
+  /// Encre chaude — remplace le noir pur pour du texte/des icônes posés sur un
+  /// remplissage clair (crème, ember clair). Un noir pur sur une teinte chaude
+  /// paraît sale ; ce brun très sombre garde le contraste sans le décalage.
+  static const Color onPrimaryFixed = Color(0xFF360F00);
+  static const Color primaryFixed = Color(0xFFFFDBC8);
+  static const Color primaryFixedDim = Color(0xFFFFB68C);
+  static const Color onPrimaryFixedVariant = Color(0xFF7A2C08);
+
   // ============ SECONDARY (Terre cuite / argile) ============
   static const Color secondary = Color(0xFFE7C3AC);
   static const Color onSecondary = Color(0xFF442A1B);
@@ -92,6 +100,7 @@ class AppColors {
   static const Color onSurface24 = Color(0x3DF3E9DF);
   static const Color onSurface38 = Color(0x61F3E9DF);
   static const Color onSurface54 = Color(0x8AF3E9DF);
+  static const Color onSurface70 = Color(0xB3F3E9DF);
 
   // ============ STATUS ============
   static const Color success = Color(0xFF9BC46A); // olive lumineux