feat(settings): storage usage tile with persistence status (#120)

One tile under Settings → General → Storage: total local usage vs the
browser's quota from navigator.storage.estimate(), the Chromium
usageDetails breakdown when available (IndexedDB = sync cache + encryption
keys + search index; Cache Storage = offline app files), and whether the
browser granted persistent storage — green "Protected" or amber "May be
evicted" with a "Keep my data" button that calls storage.persist(). That
last bit is the useful diagnostic for the KE-1 storage-eviction cluster.

No clear button: media lives in the browser's own HTTP cache (not in the
estimate, and not clearable from a page), the crypto store must never be
casually cleared, and the search-index clear already lives in Message
Search. The About page's "Clear Cache & Reload" now says it deletes this
device's encryption keys too. Hidden entirely when estimate() is missing.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01PPmy3tPq869XDW4njjVaKA

src/app/features/settings/general/General.tsx

@@ -121,6 +121,7 @@ import { previewRingtone, RINGTONE_OPTIONS } from '../../../utils/ringtones';
 import { DenoiseTester } from './DenoiseTester';
 import { SettingsSelect } from '../../../components/settings-select/SettingsSelect';
 import { isBindableCallKey } from '../../../utils/callKeybind';
+import { StorageUsage } from './StorageUsage';
 
 /**
  * P5-47 — opt-in TDS window chrome toggle (desktop only). Renders nothing in the
@@ -2741,6 +2742,7 @@ export function General({ requestClose }: GeneralProps) {
               <Editor />
               <Messages />
               <Privacy />
+              <StorageUsage />
               <SettingsSyncSection />
               <Calls />
               <AppUpdates />