Run local usage services in a supervised backend process (#40792)

* Move local usage services into a supervised backend process

* Own usage recovery and worker retirement lifetimes

* Preserve answered usage data during background refresh

* Run independent usage scans concurrently in the backend

* Limit backend startup paths to the delegated usage service

* Show usage failures through backend recovery

* Include usage failure strings in the English catalog

* Keep usage update details beside refresh failures

* Resolve usage freshness failure from the final producer snapshot

* Retain the forced refresh completion requirement

* Keep managed backend failures out of application crash reports

* Preserve usage recovery boundaries across backend reconnects

* Match the backend RPC cancellation signal in the usage seam proof

* Avoid serializing backend requests before port delivery

* Keep receiving request validation in the boundary schemas

* test: align usage transport coverage with renderer project

* fix: preserve unknown usage state and renderer retirement

* fix(usage): revalidate tracking before scan admission

* fix(usage): retry failed backend startup on demand

* test(usage): isolate stale backend ownership checks

config/scripts/static-analysis/process-boundaries/check-runtime-electron-ratchet.mjs

@@ -23,6 +23,7 @@ const ENTRY_POINTS = [
 
 // Whole lane directories cover new files automatically; only structured-chat files are plain-Node-safe inside runtime/.
 export const STRUCTURED_CHAT_LANES = [
+  { directory: ['src', 'main', 'backend'] },
   { directory: ['src', 'main', 'native-chat'] },
   { directory: ['src', 'main', 'claude'] },
   { directory: ['src', 'main', 'codex'] },