feat(calendar): add durable synchronization lifecycle

[IYENTeam]

Summary

• add production full/incremental Google Calendar synchronization and HTTP 410 recovery
• add expiration-driven watch renewal, durable trigger journal, sink-confirmed outbox retries, and deduplication
• enforce exact read-only OAuth scope, private credential/state files, bounded HTTP requests, and authenticated webhook identity
• render created/updated/cancelled Calendar events for Slack, Discord, and local routes with operational health

Verification

• cargo fmt --all -- --check
• cargo clippy --all-targets --locked -- -D warnings
• cargo test --all-targets --locked (704 unit; 16 + 17 + 7 + 2 + 1 integration targets)
• cargo build --release --locked
• cargo package --locked --allow-dirty
• five independent reviewer lanes: PASS
• real Victor Calendar create/update/delete observed through the production callback and typed localfile route; QA event removed
• deployed public health: ok=true, GitHub running, Calendar running, cursor present, outbox=0, null sync/watch errors