v0.16.53

Inbox performance diagnostics

• Adds opt-in debug timing for selected-thread render-model construction and cache-disabled direct message fetch/apply phases.
• Emits safe Server-Timing metrics from the inbox message sync route so traces can separate auth, query parsing, list, and total handler time.
• Sanitizes debug payloads so workspace, conversation, contact, phone, email, name, and body values are never logged.