Behavior-preserving restructure of the MemoEditor subsystem for simplicity
and extensibility:
- Add a data-driven command catalog (editorCommands.ts) as the single source
for formatting verbs; the toolbar, active-state hook, and WYSIWYG handle all
derive from it, so adding a verb is a one-file change.
- Add a createSuggestionExtension factory; TagSuggestion consumes it, so new
`/` or `@` triggers reuse the shared popup in ~10 lines.
- Collapse FormattingController into a single EditorController with an optional
`formatting` capability; PlainEditor is an honest textarea fallback (no faked
formatting); replace stringly-typed isActive with typed getActiveFormats.
- Move audio-recorder state out of the reducer into useAudioRecorder, keeping a
single recorderBusy flag in the store.
- Convert the editor context to an external store (useSyncExternalStore) with
per-slice subscriptions, so typing no longer re-renders the toolbar, insert
menu, or metadata.
- Extract the shared #tag lexing grammar (tag-grammar.ts) used by both the
editor tokenizer and the remark renderer.
- Remove dead reducer actions/cases and fix a preview blob-URL leak on the
upload path.
Add tests for the command catalog, suggestion factory, and autosave.
