Update docs for Discord and GitHub verifications from Warpcast API (base#416)

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## PR-Codex overview
This PR updates the documentation for the `GET
/fc/account-verifications` endpoint, clarifying its stability status and
adding a new query parameter for platform filtering.

### Detailed summary
- Updated stability note to indicate potential deprecation.
- Added `platform` query parameter to limit response to specific
platforms: `'x'`, `'github'`, or `'discord'`.
- Expanded `platform` field description in the response to include
`'github'` and `'discord'`.
- Added an example response for a verification from `github`.

> ✨ Ask PR-Codex anything about this PR by commenting with `/codex {your
question}`

<!-- end pr-codex -->

Author: goksu

docs/reference/warpcast/api.md

@@ -959,18 +959,19 @@ curl -X DELETE \
 
 `GET /fc/account-verifications`
 
-### This endpoint is not stable (beta) and very likely to have breaking changes in the future.
+### This endpoint is not stable (beta) and likely to have breaking changes in the future or get depracated.
 
 List of account verifications attested by Warpcast. Ordered by the time when the verification occurred, descending. Paginated. Not authenticated.
 
 Query parameters:
 
 - `fid` (**optional**) - limit the response to specific user
+- `platform` (**optional**) - limit the response to specific platform `'x' | 'github' | 'discord'`. Defaults to `'x'` for backwards compatibility.
 
 Returns: a `verifications` array:
 
 - `fid` - account Farcaster id
-- `platform` - platform of the verification `'x'`
+- `platform` - platform of the verification `'x' | 'github' | 'discord'`
 - `platformId` - string value representing platform identifier (generated by the platform, not Warpcast)
 - `platformUsername` - string value representing platform username
 - `verifiedAt` - UNIX time when verification took place, in seconds
@@ -986,6 +987,13 @@ Returns: a `verifications` array:
         "platformUsername": "dwr",
         "verifiedAt": 1728505748
       },
+      {
+        "fid": 3,
+        "platform": "github",
+        "platformId": "86492",
+        "platformUsername": "danromero",
+        "verifiedAt": 1728505748
+      },
       ...
     ]
   },