Fix annotate terminal startup in large folders

[backnotprop]

Summary

• exclude .claude/ and .agents/ from annotate folder file-browser scans
• cap folder file-browser scans to avoid monopolizing the Bun server on huge trees
• make the annotate WebTUI panel cancel cleanly before onReady and use the DOM renderer

Verification

• bun test packages/server/agent-terminal.test.ts packages/shared/reference-common.test.ts packages/server/reference-handlers.test.ts
• bun run typecheck
• live smoke: plannotator annotate . on this repo; /api/reference/files returned 189 files quickly and Pi spawned through WebTUI

[backnotprop]

This is now released in version 0.23.0