Roadmap: close the @pierre/trees feature gaps

[RayZhao1998]

What to build

Track the native Swift feature work required to close the most important gaps identified against the @pierre/trees documentation. The roadmap keeps TreeKit model-first and cross-platform while preserving native virtualization, accessibility, and caller-owned filesystem persistence.

Progress

• Add model-backed search and filtering #1
• Add incremental tree mutations and semantic events #2
• Complete visible-tree navigation and interaction observation #3
• Add empty-directory chain flattening #4
• Add inline rename with validation and focus restoration #5
• Add native drag and drop with path-first events #6

Delivery order

1. Search, incremental mutations, visible-tree navigation, and empty-directory flattening can begin independently.
2. Inline rename begins after mutation and navigation foundations are available.
3. Drag and drop begins after path-first mutations are available.

Acceptance criteria

• All linked implementation issues are closed with their tests and documentation complete.
• The Demo exercises search, mutations, navigation, rename, drag and drop, and flattened directory chains against the large repository fixture.
• SwiftUI, AppKit, and UIKit expose consistent shared-model semantics for every roadmap capability.
• Performance checks confirm the new functionality does not regress mounted-row reuse or large-tree interaction.
• The public documentation clearly distinguishes TreeKit-owned rendering and interaction from caller-owned filesystem enumeration, watching, persistence, and lazy loading.

Non-goals

• Web-only SSR, hydration, React hooks, DOM lifecycle, CSS variables, and Shadow DOM APIs.
• Filesystem enumeration, directory watching, persistence, or lazy child loading.
• Built-in Git status themes and icon packs; custom rows already cover these presentation concerns and they can be proposed separately if automatic ancestor aggregation becomes necessary.

Reference

• https://trees.software/docs

Blocked by

None - this issue tracks the linked work.