feat(crypto) + docs: request persistent storage; consolidate docs to 3

- index.tsx: request navigator.storage.persist() for logged-in sessions so the
  browser can't evict the IndexedDB rust-crypto store (eviction while the
  localStorage session survives resurrects the device with a blank store → the
  KE-1 "one time key already exists" upload storm). Guarded, checks persisted()
  first, best-effort.
- Docs: remove HANDOFF_ELEMENT_CALL_FORK.md, LOTUS_E2EE_INVESTIGATION.md, and
  LOTUS_BUGS.md. Port their live content into the three kept docs — verification
  backlog → LOTUS_TESTING; open bugs + E2EE (KE-1..4) + an Element Call fork
  operational reference (publish steps + io.lotus action catalog) → LOTUS_TODO.
  Fix all dangling references (README, code comments, cross-doc links). Full
  history of the removed docs remains in git.

Gates: tsc/eslint/prettier clean, build OK, 665 tests.

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

src/app/plugins/call/CallControl.ts

@@ -34,7 +34,7 @@ export class CallControl extends EventEmitter implements CallControlState {
   // P6-2: mirrors CallEmbed.joined. Set true from forceState(), which CallEmbed
   // invokes only from onCallJoined(). Gates io.lotus.set_deafen so we never send
   // before the fork's widget handler mounts (pre-join sends pend to a 10s
-  // timeout — HANDOFF_ELEMENT_CALL_FORK.md §12.1 F1).
+  // timeout — io.lotus toWidget actions must only be sent after call-join).
   private joined = false;
 
   private get document(): Document | undefined {