feat(toolbar): add ais.index block support for index-scoped widgets

[sarahdayan]

Summary

Adds full toolbar support for ais.index blocks introduced in #25. Users can manage index-scoped widget hierarchies through both the manual UI and the AI assistant.

Key changes:

• Auto-wrapping: index-dependent widgets are automatically placed inside ais.index blocks (creates one if none exists, appends to the last one otherwise)
• Path-based addressing: all state callbacks use BlockPath ([parentIdx, childIdx]) instead of flat indices
• New IndexBlockGroup component: grouped container showing index params + nested child widgets + scoped "Add Widget" button
• Move between indices: child widgets can be moved between index blocks via a <select> dropdown
• AI tools updated: path-based addressing, target_index validation, move_widget tool, parsePath hardening (rejects empty strings, negative indices, 3+ levels)
• AddBlockResult return type: onAddBlock returns { path, indexCreated } so the AI tool can prompt for index name without relying on stale React state

Note

No new widget was added (aside from index). The preview images below used a dummy searchBox widget for manual tests, but this PR doesn't include it.

Files changed

File	What
types.ts	BlockPath, AddBlockResult, optional container, indexId
widget-types.tsx	ais.index entry, indexIndependent flag, columns option
app.tsx	Auto-wrap logic, path-based callbacks, onMoveBlock, helpers
panel.tsx	Nested rendering, widget count, expand/collapse state machine
index-block-group.tsx	New — grouped container for index blocks
block-card.tsx	Index selector for moving widgets, label accessibility fix
block-editor.tsx	CSS grid layout via columns config
add-widget-popover.tsx	filter prop to exclude ais.index in scoped menus
ai/tools.ts	Path addressing, target_index validation, move_widget, parsePath hardening
ai/system-prompt.ts	Conciseness guidance
ai-chat.tsx	Updated prop types
ai-tools.test.ts	11 new tests (44 → 55)

Preview