无缝 UI 变形循环（Beat-synced Playwright + FFmpeg）

Use the full template for a beat-synced UI morph loop rendered from a single HTML scene with Playwright and FFmpeg.

Inputs I will provide: 8–12 UI states, one accent color (or monochrome), and a royalty-free track near 120 BPM.

Visual rules:
- 1440×1440 warm-gray canvas, Geist typography.
- ONE continuously morphing shell (never cut into separate layers); content swaps inside with short blur only.
- Visible cursor causes EVERY click and drag; drags set values from cursor position while held, release springs from current state.
- Restrained springs and camera zooms; NO bounce easing, particles, glow, chrome gradients, mismatched icon weights, dead air, or template SaaS look.

Beat map (7 bars): button → loader → check → dynamic island → player play/pause → scrubber drag → overextended volume slider → toggle → liquid tab indicator → self-drawing chart + tooltips → command palette type/filter → Enter → toast → return to starting button.

Engine:
- Single HTML file; seek(t) computes ALL properties; no CSS transitions, no setInterval, no hidden frame state.
- Closed-form spring step responses with superposition for multi-step targets; independent edge springs for tabs/toggles.

Render:
- Analyze audio in NumPy; start on downbeat; UI clicks on measured peaks.
- Playwright: 4 subframes per output frame; FFmpeg tmix → 60fps motion blur.
- Before full render: one still per beat; fix off-grid timing and legibility; avoid will-change on camera-scaled nodes; separate in/out text timing; last frame MUST match first (cursor pos + velocity).