fix: isolate global timeline and audio stores per project root

[ubugeeei]

Finding

Timeline/audio state is stored in module-level globals. HMR, hidden probes, multiple roots, or failed unmounts can leave stale or duplicate state.

Evidence

• src/lib/timeline.tsx global timeline state.
• src/lib/audio-plan.ts global audio segment state.
• render settings hidden project render uses the same process state.

Acceptance criteria

• Scope timeline/audio registries to a Project root/session.
• Cleanup deterministically on unmount/errors.
• Keep current public APIs compatible.

[ubugeeei]

対応済みです。修正は PR #1 / commit 9cf4498 に反映済みです。