[abruption]

Closes #172

What changed

• Timestamp opt-in receiver and Relay lifecycle events with UTC epoch milliseconds.
• Generate a fresh UUIDv4 for each client Relay setup attempt; carry it in a bounded WebSocket header, Relay room metadata, and the attach notice only for capable peers. Record it in client success/failure metadata and receiver attach/peer-TLS events.
• Keep legacy bare attach frames valid during rolling upgrades. Missing or ambiguous evidence remains unattributed.
• Document the privacy and attribution boundary in four locales.

No service or production configuration changes.

Verification

• Full local suite: 515 run, 504 passed, 11 skipped (Python 3.14.7, websockets 17.1).
• Real loopback Relay test joins client, Relay, and receiver by one ID and checks timestamp/privacy; legacy and mixed-version attach tests pass.
• Documentation i18n checks pass.

Known existing full-suite sqlite ResourceWarning occurs in test_control_backup_snapshot.py and is unrelated to this change.