Task/Issue URL:
https://app.asana.com/1/137249556945/project/1205648422731273/task/1217461705260962?focus=true
Tech Design URL (if applicable): 
API Proposals URL(s) (if applicable): None

### Description

`auth-token-refresh` wide event predates pixel registry rollout in this
repo and we never added a pixel registry entry. This PR closes this gap.

### Steps to test this PR

QA-no optional

### UI changes
<!-- CURSOR_SUMMARY -->
---

> [!NOTE]
> **Low Risk**
> Analytics schema addition only; no authentication or token-handling
code changes in this PR.
> 
> **Overview**
> Adds a new **wide event** pixel schema at
`wide_auth_token_refresh.json5` for monitoring **auth v2 access token
refresh** end-to-end (read refresh token → JWKS fetch → token request →
validation → save).
> 
> The definition follows the same wide-pixel pattern as other features
(standard `widePixel*` parameters, `daily_count_short` / `form_factor`
suffixes). **Feature-specific `feature.data.ext` fields** capture
context at refresh start (subscription status, process name, VPN
enabled/running), cross-process **serialization**
(`serialization_enabled`, `lock_outcome`, bucketed lock-wait latency),
**bucketed latencies** for JWKS fetch, token request, and total
duration, backend **`backend_error_response`**, Play login fallback
**`play_login_error`**, **`failure_reason`** on failures, and **step
flags** (`lock_acquire`, `token_read`, `jwks_fetch`, `token_request`,
`token_validation`, `play_login`).
> 
> This is **schema-only** in PixelDefinitions; it does not change client
auth logic in this diff.
> 
> <sup>Reviewed by [Cursor Bugbot](https://cursor.com/bugbot) for commit
e898f4d44dd836b4512bc1c21b803fa1c9f20ebb. Bugbot is set up for automated
code reviews on this repo. Configure
[here](https://www.cursor.com/dashboard/bugbot).</sup>
<!-- /CURSOR_SUMMARY -->

Co-authored-by: Claude Fable 5 <noreply@anthropic.com>