refactor: extract TUI into @perstack/tui-components and @perstack/tui

[FL4TLiN3]

Summary

• Move all React/Ink TUI code from apps/perstack/src/tui/ into packages/tui-components/src/ — components, execution, selection, context, hooks, types, utils
• Create new @perstack/tui package with startHandler and supporting lib code (context, run-manager, interactive, get-env, perstack-toml, provider-config)
• Eliminate cross-app import: apps/create-expert now imports startHandler from @perstack/tui instead of perstack/start

Dependency graph (after)

@perstack/core   @perstack/react   ink   react
       ↓               ↓             ↓     ↓
  ┌─────────────────────────────────────────────┐
  │        @perstack/tui-components              │
  └─────────────────────────────────────────────┘
                        ↑
  ┌─────────────────────────────────────────────┐
  │              @perstack/tui                   │
  └─────────────────────────────────────────────┘
           ↑                       ↑
    apps/perstack            apps/create-expert

Test plan

• pnpm typecheck — 19/19 packages pass
• pnpm build — 19/19 packages pass
• pnpm test — 101 test files, 1101 tests pass
• pnpm format-and-lint — no new errors (only pre-existing warnings)

🤖 Generated with Claude Code