Add quote resurfacing and spaced review

[mokhov]

Problem

Saved quotes disappear into an archive and are rarely revisited after the book is finished.

Proposed behavior

Provide configurable random, daily, themed, and spaced-repetition review of saved quotes.

Acceptance criteria

• Readers can review quotes randomly, by book, by tag, or through a spaced schedule.
• Each review can jump back to the exact source range.
• Readers can keep, snooze, master, or remove a review item.
• Frequency and notifications are optional and disabled by default.
• Review state remains private, local, and compatible with annotation sync.