refactor(tui): compose tab pulse layers

[opencode-agent]

Summary

• replace the mirrored outer* tab-pulse props with composable primary and edge layer descriptions
• share one frame-deduplicated pulse timeline across every vertical surface for a tab so separators, title, and detail rows travel in phase
• centralize pulse state and palette reconciliation in one PulseLayer abstraction

Performance

• shared timelines advance each tab animation once per renderer frame instead of once per painted surface
• layer objects reconcile only when reactive inputs change; per-cell painting remains unchanged

Checks

• bun test test/component/tab-pulse.test.tsx test/context/session-tabs.test.tsx test/context/session-tabs-model.test.ts
• bun typecheck
• focused Prettier and oxlint checks (oxlint reports two pre-existing non-null assertion warnings in session-tabs.tsx)
• OpenCode Drive recording against the updated commit
• two focused sub-agent reviews; timeline lifecycle finding addressed

Requested by: @kitlangton (Kit Langton via Slack)