fix: batch Resume UI layer installation

[tt-a1i]

Summary

• batch the subagent, suggestion, and workflow editor layers into one post-bind setEditorComponent write per TUI session
• rebuild the composed factory for a fresh Resume runtime instead of retaining instance-local guards or stale session closures
• keep the task widget mounted while it is visible, render from the live task snapshot, and request a repaint for content changes

Why

Pi owns /resume: it clears extension UI, replaces the Session runtime, and emits session_start for the new runtime. The old PR #13 tried to suppress repeated installs with booleans stored inside each extension instance, but those booleans reset on Resume. Its task guard could also freeze the first snapshot.

This change works with Pi's lifecycle: editor contributors register their layers on the runtime EventBus, one coordinator batches the UI installation after all session_start handlers, and shutdown removes only layers that were actually registered.

Replaces #13.

Test plan

• bun run check
• bun run test — 715 Node tests and 29 Vitest tests
• npm pack --dry-run --ignore-scripts --json — runtime coordinator included, test excluded
• regression test creates a fresh harness for the resumed runtime and verifies one editor UI write per Session
• task regression test verifies one mounted widget renders newly added and transitioned tasks from live state