[ADM 7] Restore Insert/Delete and canvas DnD - #212

Summary

• consolidate insert and move behavior on the canonical NodePlacement model, with structured validation for invalid references, root/self/descendant moves, and no-op placements
• restore contextual ZORA Insert and Delete authoring, including blueprint defaults, selection updates, confirmation, and complete subtree binding cleanup
• add native/web canvas drag and drop using @ankhorage/react-native-reanimated-dnd-web directly, with a 48-point handle, measured ghost, Runtime-backed targets, invalid-zone feedback, and deterministic adapter-session remounts after drop or cancellation
• enforce that active drag geometry exists only while Edit mode, selection, and the current manifest root still own the dragged node
• remove obsolete @ankhorage/studio/dnd* wrappers, directional tree mutation APIs, and their stale generated sequence artifact
• update package documentation, generated Paradox output, and add a minor changeset

Why

ADM 7 needs Insert, Delete, and canvas movement to use the same manifest-driven authoring primitives as generated Ankhorage apps. The previous directional and wrapper APIs duplicated placement behavior and kept Studio farther from the normal Runtime/ZORA application model.

Impact

Studio now injects the generated app's component metadata, persists authoring operations through one canonical placement path, and composes the maintained cross-platform DnD adapter directly. Package-neutral placement and drag-session helpers remain independent of React, ZORA implementations, and host persistence.

Validation

• bun run build
• bun run lint:fix
• bun run test — 496 passed, 3 conditional skips
• bun run knip
• bun run typecheck
• bun run format:check
• bun run docs
• bun run changeset:status
• bun run test:smoke:studio-web — 1 passed, 54 assertions
• bun run test:e2e:generated-app-web — 7 passed, 297 assertions

Closes #122