v0.1.15

Patch release for larger Notes backups and better backup failure reporting.\n\n- Raises server JSON sync request limit to 25 MB for larger note backup payloads.\n- Shows HTTP failure details in the Notes backup status instead of a generic backup failure.\n- Bumps server and Notes release metadata to 0.1.15.\n\nValidation: notes check, backend tests, suite build, notes build, Android APK build/sign/verify, Docker linux/amd64 build.