Add extended diagnostics logging

- Electron crash handlers (render-process-gone, child-process-gone,
  unresponsive/responsive, process warnings) with a circuit-breaker
  auto-reload for renderer crashes
- Renderer error capture (window.onerror, unhandledrejection, React
  ErrorBoundary) forwarded to the main log via a one-way IPC channel
- Memory-pressure heartbeat measured against the V8 heap_size_limit
- Gated DEBUG log level (RD_DEBUG) and an in-memory ring of recent
  WARN/ERROR lines, exposed via the /errors endpoint and support bundle
- Disk-error classification (ENOSPC etc.) on download failures and
  integrity-check pass/fail logging

src/shared/preload-api.ts

@@ -9,6 +9,7 @@ import type {
   DuplicatePolicy,
   HistoryEntry,
   PackagePriority,
+  RendererErrorReport,
   SessionStats,
   StartConflictEntry,
   StartConflictResolutionResult,
@@ -85,6 +86,7 @@ export interface ElectronApi {
   skipItems: (itemIds: string[]) => Promise<void>;
   resetItems: (itemIds: string[]) => Promise<void>;
   startItems: (itemIds: string[]) => Promise<void>;
+  reportRendererError: (report: RendererErrorReport) => void;
   onStateUpdate: (callback: (snapshot: UiSnapshot) => void) => () => void;
   onClipboardDetected: (callback: (links: string[]) => void) => () => void;
   onUpdateInstallProgress: (callback: (progress: UpdateInstallProgress) => void) => () => void;