d87ad36278
Replaces the textarea-based editor with a Tiptap v3 contenteditable. The custom Mention node uses personId/displayName attrs (instead of Tiptap's default id/label) so mentionSerializer round-trips cleanly. AC-1 fix (issue #372): when the user types '@Aug' and selects 'Auguste Raddatz', the mention node stores displayName: 'Aug' (the typed query) — not the person's DB display name. This preserves archival fidelity of the original transcription. The MentionDropdown is mounted imperatively on document.body via Svelte 5's mount(). Its three pieces of dynamic state (items, command, clientRect) are passed as a single $state proxy (model) because Svelte 5's mount() does not return prop accessors. Spec is fully rewritten — all old tests used document.querySelector ('textarea') which is dead after the migration. Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>