Edit files in a context document tree

Edit files in a tree.

Supports three edit kinds — all persist to the tree_edits table so they survive subsequent regens:

• files: content edits (map of path → new content)
• renames: rename edits (map of old path → new path)
• deletions: soft-delete (list of paths)

Editable when status is COMPLETED or PUBLISHED. PROCESSING is rejected (the workflow is mid-write); FAILED has nothing meaningful to edit. The tree's files JSONB is updated in-place so the dashboard sees immediate results without waiting for the next regen.