feat: replace Remotion with custom Bradly Engine (Phases 1-3)

- Phase 1: Custom animation engine (interpolate, spring, Easing)
- Phase 2: Custom composition components (AbsoluteFill, Sequence, Img, Video, Audio)
- Phase 3: BradlyPlayer with rAF frame loop, imperative API, controls

Migrated 24 files from remotion/@remotion/player imports to src/engine/.
All type errors from migration resolved. Pre-existing errors remain unchanged.

src/components/properties/AudioLayerPanel.tsx

@@ -1,7 +1,7 @@
 import React, { RefObject } from 'react';
 import { Music } from 'lucide-react';
 import { TimelineElement } from '../../types';
-import { PlayerRef } from '@remotion/player';
+import type { BradlyPlayerRef } from '../../engine/player';
 import { uploadMedia } from '../../utils/mediaUploader';
 import { FileDropZone } from '../ui/FileDropZone';
 import { getAudioDuration, durationToFrames } from '../../utils/audioMetadata';
@@ -10,7 +10,7 @@ interface AudioLayerPanelProps {
   activeLayerId: string;
   setTimelineElements: React.Dispatch<React.SetStateAction<TimelineElement[]>>;
   timelineElements: TimelineElement[];
-  playerRef: RefObject<PlayerRef | null>;
+  playerRef: RefObject<BradlyPlayerRef | null>;
   endFrameLimit?: number;
 }