fix(app): phase-lock harmonic dot SMIL + crossfade done-dot transition

[jeonghun-jj-lee]

Summary

Phase-lock the harmonic dot's SMIL animation to a global modular clock so remounts pick up mid-morph instead of restarting from the ring. Add a 150ms opacity crossfade on the done-dot for a smooth running→done handoff.

Changes

File	Change
packages/ui/src/amicode/harmonic-geometry.ts	New smilBeginOffset() — computes -(Date.now() % CYCLE_MS)ms
packages/ui/src/amicode/harmonic-dot.tsx	Wire begin={begin} into both <animate> elements
packages/app/src/index.css	transition: opacity 150ms ease-out on done-dot
packages/ui/src/amicode/harmonic-geometry.test.ts	Phase-lock offset correctness tests
packages/app/src/pages/session/timeline/travelling-dot.test.ts	Done-dot crossfade regression guard

Testing

• packages/ui: 488 pass, 0 fail
• packages/app: 900 pass, 9 fail (pre-existing SolidJS use export issues, unchanged)
• Typecheck: 30/30 pass

Closes #273

[coderabbitai]

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