Phase 7: lock-screen expand (state L2)

[tirthfx]

What changed

Phase 7 of the dual-surface build: click-to-expand on the lock screen (PRD §3.2 state L2, reference image 2).

• Clicking the widget's art/track expands: the wallpaper dims toward black, the album art scales up to center via a matched-geometry hero morph, and a frosted control pill (title/artist, scrubber, transport) settles below it.
• Click-away on the dimmed backdrop or Esc collapses back to the widget symmetrically; Esc at the widget level dismisses the whole surface.
• New LockScreenUIState (widget/expanded/lyrics presentation + shared spring, mirroring the notch's NotchUIState), LockScreenExpandedView, and a shared TransportButtons component now reused by both the widget and the expanded view (and ScrubberView continues to be shared with the notch).

Why

Continues Surface B toward the reference flow: L1 widget (done) → L2 expand (this) → L3 swipe-to-lyrics (Phase 8).

Base

Stacked on phase-6-lockscreen-widget (open PR #6, verified/unmerged). Diff is Phase 7 only. Merge the stack (5 → 6 → 7) in order, or rebase onto main.

Notes for review — needs your eyes in Xcode

• Visuals unverifiable headlessly (lock screen blocks synthesized input/screenshots). Confirmed: builds clean, launches without crashing, notch unaffected. Please run it, play a track, ⌃⌘L, then click the album art: expect the wallpaper to dim, art to grow to center, controls pill below; click empty space or Esc to collapse.
• The expand uses the same .smooth spring as the notch's open/close, so the two surfaces should feel identical.
• .lyrics currently renders the expanded view as a placeholder — the real lyrics panel lands in Phase 8.

🤖 Generated with Claude Code

[gemini-code-assist]

Code Review

This pull request introduces an expanded lock-screen now-playing view (LockScreenExpandedView) and manages transitions between the compact widget and expanded states using a new LockScreenUIState and matched geometry effects. It also refactors transport controls into a shared TransportButtons component. Feedback includes marking the onDismiss closure in PseudoLockScreenController as @MainActor for concurrency safety and removing a redundant default parameter in LockScreenNowPlayingWidget.

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[gemini-code-assist]

To ensure strict concurrency safety and compatibility with Swift 6, explicitly mark the onDismiss closure as @MainActor. Since PseudoLockScreenController is @MainActor isolated, calling handleEscape() from a non-isolated closure context can trigger compiler warnings or errors.

Suggested change

	window.onDismiss = { [weak self] in self?.handleEscape() }
	window.onDismiss = { @MainActor [weak self] in self?.handleEscape() }

[gemini-code-assist]

The primarySize parameter is redundant here because TransportButtons already defaults primarySize to 26. Removing it simplifies the call site.

            TransportButtons(
                isPlaying: nowPlaying.isPlaying,
                onPrevious: onPrevious,
                onPlayPause: onPlayPause,
                onNext: onNext
            )