Epic/rich editor

[codenem]

Summary by cubic

Introduces a new TipTap-based rich text editor for document descriptions with block menus, inline tools, and advanced tables, plus debounced autosave. Adds a backend mutation to save version content and makes document content optional on create.

• New Features

  • New RichEditor in @probo/ui using @tiptap/react and @floating-ui/react with slash commands, block/options menus, and a bubble toolbar.
  • Advanced tables: row/column/cell menus, drag to reorder, split/merge cells, header rows/cols, and a selection overlay.
  • Link UX: inline editing and Cmd/Ctrl+click to open.
  • Debounced autosave (1s) for draft versions via a new mutation; editor is read-only for non-draft versions.
  • Full-height layout and improved focus/scroll behavior.

• Migration

  • GraphQL: use updateDocumentVersionContent(input) to persist editor content for a version.
  • CreateDocumentInput.content is now optional; clients can omit it or continue sending it.

^{Written for commit 260a192. Summary will update on new commits.}