Add intercom contact ID shortcut

[dataforxyz]

Summary

• add /intercom-id and Alt+I to copy this session's stable intercom contact ID
• fall back to inserting the handoff snippet when clipboard copy is unavailable
• cover duplicate-name targeting and wl-copy daemonizing behavior in tests

Tests

• npx tsx --test broker/client.test.ts broker/framing.test.ts broker/paths.test.ts broker/spawn.test.ts clipboard.test.ts config.test.ts reply-tracker.test.ts intercom.integration.test.ts test/inline-message.test.ts test/overlay-width.test.ts