Add a private reading journal and book wrap-up

[mokhov]

Problem

Progress and annotations do not capture the reader's evolving thoughts, mood, character memory, or final impression of a book.

Proposed behavior

Provide private session entries, character notes, custom ratings, and an optional completion summary.

Acceptance criteria

• Readers can record session thoughts and an optional mood without interrupting reading.
• Character notes can link to a stable passage and remain separate from generated entity data.
• Finished books support custom rating dimensions and a private summary.
• Journal entries are searchable and exportable.
• All journal data remains local unless the reader explicitly enables existing sync.