feat(inbox): Capture "Signal source connected" analytics event

[Twixes]

Summary

• Adds a new Signal source connected analytics event, fired from both signal-source connection paths in useSignalSourceManager: the direct toggle (non-warehouse sources) and the post-DataSourceSetup-wizard completion (warehouse sources).
• Event carries source_product, is_first_connection (brand-new config vs. re-enable of an existing one), and via_setup_wizard (warehouse OAuth path vs. plain toggle).
• Closes a gap surfaced when trying to measure inbox onboarding — there was no event firing on the actual source-connected moment. Now we can build a first-time-for-user trend (e.g. "inbox users onboarded") and subscribe a team channel to a daily snapshot.

Test plan

• Toggle on error_tracking from the Inbox sources settings → confirm Signal source connected fires once with source_product: "error_tracking", is_first_connection: true, via_setup_wizard: false. Toggle off then on again → second firing has is_first_connection: false.
• Toggle on session_replay → same flow as above (non-warehouse path).
• Connect github (or any warehouse source) via the DataSourceSetup wizard end-to-end → confirm one firing on completion with via_setup_wizard: true and is_first_connection: true.
• Disable a previously enabled source → confirm no event fires (we only track connections, not disconnections).
• If the API call inside handleSetupComplete fails → confirm the event does not fire (it lives inside the try block, before the catch).

[greptile-apps]

Prompt To Fix All With AI

Fix the following 1 code review issue. Work through them one at a time, proposing concise fixes.

---

### Issue 1 of 1
apps/code/src/renderer/features/inbox/hooks/useSignalSourceManager.ts:431-435
The `track` call fires unconditionally inside the `try` block — even when `existing` is already truthy **and** `existing.enabled` is already `true`. In that case neither `createSignalSourceConfig` nor `updateSignalSourceConfig` is invoked, so no actual connection happened, yet a `Signal source connected` event is emitted. A concrete path to this state: a warehouse source's external-data-source row is deleted externally while the signal-source config stays enabled; the next toggle attempt opens the wizard, and completing it fires a spurious analytics event.

```suggestion
        if (!existing || !existing.enabled) {
          track(ANALYTICS_EVENTS.SIGNAL_SOURCE_CONNECTED, {
            source_product: completedSource,
            is_first_connection: !existing,
            via_setup_wizard: true,
          });
        }
```

_{Reviews (1): Last reviewed commit: "feat(inbox): Capture "Signal source conn..." | Re-trigger Greptile}