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>

README.md

@@ -180,10 +180,10 @@ avatar decorations on EC video tiles, and a native transparent background.
 (`io.lotus.inject_audio` → in-call soundboard) and quality controls
 (`io.lotus.set_quality`).
 
-The full plan and integration map is in
-**[`HANDOFF_ELEMENT_CALL_FORK.md`](HANDOFF_ELEMENT_CALL_FORK.md)**; infra/hosting +
-build-pipeline notes live in the `LotusGuild/matrix` repo README. Search the docs
-for the **`[EC-FORK]`** tag to find every related note.
+The fork's `io.lotus.*` action catalog + the publish procedure are in
+**[`LOTUS_TODO.md`](LOTUS_TODO.md)** ("Element Call fork — operational reference");
+infra/hosting + build-pipeline notes live in the `LotusGuild/matrix` repo README.
+Search the docs for the **`[EC-FORK]`** tag to find every related note.
 
 ### Build