Task/Issue URL:
https://app.asana.com/1/137249556945/project/1212810093780571/task/1216783639447263?focus=true
Tech Design URL (if applicable): 

### Description

Adds pixels for when a user changes the after-inactivity "on app launch"
option
(New Tab Page / Last Opened Tab / Specific Page).

### Steps to test this PR
- [x] Filter on “pixel sent” in logcat
- [x] Open Settings → General → On app launch and pick each
option → the matching `m_ntp_after_idle_launch_option_<option>_count`
fires
      (and `_daily` once/day)

### UI changes
Telemetry only.
<!-- CURSOR_SUMMARY -->
---

> [!NOTE]
> **Low Risk**
> Analytics-only changes in settings; no auth, data handling, or
launch-behavior logic changes beyond firing pixels after the existing
persist path.
> 
> **Overview**
> Adds **telemetry** when users pick an after-inactivity launch option
on the Show on App Launch settings screen: **New Tab Page**, **Last
Opened Tab**, or **Specific Page** (custom URL).
> 
> Three new pixel definitions land in `ntp_after_idle.json5`, with
matching `ShowOnAppLaunchPixelName` entries.
`ShowOnAppLaunchViewModel.onShowOnAppLaunchOptionChanged` still persists
the choice, then fires a **count** and **daily** pixel per option (same
pattern as the Return To Last Tab toggle). Unit tests assert the correct
pixels fire for each option.
> 
> <sup>Reviewed by [Cursor Bugbot](https://cursor.com/bugbot) for commit
4160dc41e6e94993783492dc498b7599acef10f6. Bugbot is set up for automated
code reviews on this repo. Configure
[here](https://www.cursor.com/dashboard/bugbot).</sup>
<!-- /CURSOR_SUMMARY -->