Refactor big IPC handlers (#3457)

## Summary
- Split app runtime process/proxy/cloud sandbox behavior out of
app_handlers into an app runtime service.
- Move chat attachment delivery policy and formatting out of
chat_stream_handlers into a chat attachment service.
- Includes the existing Sentry Electron init/dependency changes that
were already present in the working tree when pushing.

## Test plan
- npm run fmt
- npm run lint:fix
- npm run ts
- npm test

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Author: wwwillchen

rules/electron-ipc.md

@@ -77,6 +77,7 @@ writeSettings({
 - For **non-bug** failures (validation, not found, auth, user refusal, etc.), prefer `DyadError` with the right `DyadErrorKind` so PostHog does not flood with `$exception` events — see [rules/dyad-errors.md](dyad-errors.md).
 - Use `createTypedHandler(contract, handler)` which validates inputs at runtime via Zod.
 - Avoid unguarded top-level `app.on(...)` or similar Electron API calls in modules that are imported broadly by tests. Many unit tests mock only the Electron APIs they touch, so prefer guarded calls like `app?.on?.(...)` or move event registration behind an explicit initialization function.
+- When splitting large handlers behind service boundaries, leave the handler responsible for IPC registration and request orchestration while moving runtime/policy logic into `src/ipc/services/*`. Preserve any intentional module side effects in the extracted service, such as `fixPath()` for child process PATH setup.
 
 ## React Query key factory