Add rich notes with voice and pen input

[mokhov]

Problem

Text entry is not always the most natural way to capture a thought, especially on tablets or while listening.

Proposed behavior

Allow speech-to-text notes and stylus strokes anchored to a quote, bookmark, or reading location.

Acceptance criteria

• Voice transcription begins only after explicit permission and confirmation.
• Pen strokes can be drawn, erased, recolored, and attached to a stable anchor.
• Handwriting remains discoverable after repagination through a visible anchor marker.
• Unsupported input methods fall back to ordinary text notes.
• Rich-note data remains local and is included in backup or sync without losing its anchor.