docs(rum): re-verify RUM_FEATURE.md after the appHangThreshold doc-comment change

`make feature-docs-verify` flagged RUM_FEATURE.md as stale: `RUMConfiguration.swift` is a
tracked file and this branch amends the `appHangThreshold` doc-comment, so the baseline
`verified_against_commit` no longer covers the public API surface.

Mirror the source doc-comment in the App hangs configuration entry and bump the
frontmatter baseline. The Feature Docs Verify CI job only runs on release/hotfix
branches, so this would otherwise have surfaced at release time.

Author: Valpertui

DatadogRUM/RUM_FEATURE.md

@@ -1,7 +1,7 @@
 ---
-last_updated: 2026-08-12
+last_updated: 2026-08-14
 sdk_version: 3.15.0
-verified_against_commit: dc80cf268
+verified_against_commit: 83757b8fb
 tracked_files:
   - DatadogRUM/Sources/RUM.swift
   - DatadogRUM/Sources/RUMConfiguration.swift
@@ -250,7 +250,7 @@ Requires configuration to be set, otherwise disabled by default:
 
 ### Performance Monitoring
 - **Long tasks**: `longTaskThreshold` (default: 0.1s)
-- **App hangs**: `appHangThreshold` (default: nil/disabled)
+- **App hangs**: `appHangThreshold` (default: nil/disabled) — stack traces require Crash Reporting, and can be opted out of with `CrashReporting.Configuration.appHangBacktraceEnabled`
 - **Vitals**: `vitalsUpdateFrequency` (default: .average)
 - **Slow frames**: `trackSlowFrames` (default: true) — captures view hitches and attaches them to the corresponding RUM view