Fix H3/L30/L44/L60/L90/L25/L32 polish: dependencies, naming, consistency

L30: Remove redundant loading=lazy from MediaThumb images inside the
     virtualizer which only mounts visible rows anyway.
L44: electron-builder.yml now excludes the actual eslint.config.js and
     .prettierrc rather than non-existent legacy .eslintrc/.prettierrc.yaml.
L60: IpcChannels.externalUrl renamed from external-url to app:external-url
     to match every other channel name category prefix.
L90: settings.ts sanitizeOptions now uses (ARR as readonly string[]).includes
     pattern consistently with setSettings; removes the as-never hack.

typecheck + 242 tests + eslint + prettier green.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

src/shared/ipc.ts

@@ -56,7 +56,7 @@ export const IpcChannels = {
   preloadBridgeFailure: 'preload:bridge-failure',
   /** main → renderer push channel: a URL handed to AeroFetch from outside the app
    *  (the aerofetch:// protocol, or a .url file via Explorer's "Send to" menu) */
-  externalUrl: 'external-url',
+  externalUrl: 'app:external-url',
   // --- Sources & media-manager indexing (Pinchflat-style, see ROADMAP-PINCHFLAT.md) ---
   sourcesList: 'sources:list',
   sourceIndex: 'sources:index',