fix: remove reader progress debounce

[everpcpc]

Summary

• Remove per-book debounce for page progress dispatch to reduce stalls when closing the reader after reading multiple books.
• Keep in-flight coalescing so rapid page turns still collapse to the latest pending update.
• Update SwiftData progress cache asynchronously after server sync (token-guarded) so reader-close waits are not blocked by local DB work.

Testing

• make build-ios
• make build-macos
• make build-tvos