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>

LOTUS_FEATURES.md

@@ -330,7 +330,7 @@ Users can set a custom background color for `@mention` chips that highlight thei
 > pre-built npm bundle. Several in-call behaviors below are now first-class
 > source changes rather than DOM/widget hacks. Background, plan, and the Phase-2
 > work list are in
-> [`HANDOFF_ELEMENT_CALL_FORK.md`](./HANDOFF_ELEMENT_CALL_FORK.md).
+> the Element Call fork reference in [`LOTUS_TODO.md`](./LOTUS_TODO.md).
 
 ### Element Call — Self-Built Fork (`0.20.1-lotus.1`)
 
@@ -1235,7 +1235,7 @@ The session persists as ONE atomic `cinny_session_v1` JSON write (previously ~10
 
 ### Crypto Diagnostics (E2EE investigation kit)
 
-**Settings → Developer Tools → Crypto Diagnostics**: a capture-only ring buffer (max 200) hooks `console.warn/error` for E2EE failure signatures (OTK upload conflicts, missing call media keys, decryption errors, delayed-event timeouts) and downloads a JSON report — the evidence input for the KE-1→4 investigation. Companion runbook: [`LOTUS_E2EE_INVESTIGATION.md`](./LOTUS_E2EE_INVESTIGATION.md). `utils/cryptoDiagLog.ts`, `features/settings/developer/CryptoDiagnostics.tsx`.
+**Settings → Developer Tools → Crypto Diagnostics**: a capture-only ring buffer (max 200) hooks `console.warn/error` for E2EE failure signatures (OTK upload conflicts, missing call media keys, decryption errors, delayed-event timeouts) and downloads a JSON report — the evidence input for the KE-1→4 investigation. Companion diagnosis: the Encryption / E2EE section of [`LOTUS_TODO.md`](./LOTUS_TODO.md). `utils/cryptoDiagLog.ts`, `features/settings/developer/CryptoDiagnostics.tsx`.
 
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