feat(master-ui): replace list Compact with Optimize (merge+compact+index)

[beinan]

Summary

• The experiment list's per-row Compact button becomes Optimize, which enqueues the full maintenance sequence for that experiment in order: merge_wal → compact → index_id
• All three go through the unified task queue (compact now enqueues a task instead of hitting the legacy /compact bridge), so progress is visible in one place; clicking switches to the queue view
• The detail drawer keeps its three individual buttons (Compact / Merge WAL / Index id) unchanged

Test plan

• npm run build (tsc + vite) passes
• Manual: in the experiment list, click Optimize on a row → queue view shows three tasks (merge_wal, compact, index_id) queued → running → done in order
• Manual: open an experiment's detail drawer → the three individual buttons still work independently

🤖 Generated with Claude Code

[beinan]

Follow-up: fixed a gate-conflict found during e2e verification.

Optimize enqueues merge_wal → compact → index_id. Because the scheduler runs tasks concurrently (task_concurrency=4) and compact + index_id share the per-experiment base-table write gate, index_id was failing immediately with "a base-table write is already in progress".

Fix: task dependencies. compact now depends on merge_wal, index_id depends on compact, so the chain runs strictly in order.

• TaskRecord/EnqueueTaskRequest gain optional depends_on: [task_id].
• The dispatcher resolves deps before taking a semaphore permit (avoids deadlock at concurrency 1): defers+requeues while a dep is Queued/Running, marks the dependent Failed if a dep Failed.
• OptimizeButton chains the three enqueues by captured task id.
• New scheduler tests: dependent_task_runs_after_dependency_done, dependent_skipped_when_dependency_fails.