docs: add Element Call fork handoff + tag all EC-FORK references

Captures the plan to fork element-hq/element-call and build it from source for
true ownership of the in-call experience (decorations, focus/screenshare,
reconnect mic, native theming, call-audio injection) — none of which are fixable
against the prebuilt @element-hq/element-call-embedded bundle we ship today.

- New HANDOFF_ELEMENT_CALL_FORK.md: self-contained plan for a fresh session
  (current architecture, full file inventory, phases, new-repo decision, the
  denoise-shim interaction, doc corrections).
- Tagged every related note with [EC-FORK] + links: README (For Developers),
  LOTUS_BUGS (EC limitations), LOTUS_TODO (soundboard, denoise, soundboard
  cross-origin correction), LOTUS_FEATURES (call section).

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

LOTUS_BUGS.md

@@ -38,9 +38,15 @@ Implemented and gate-green; confirm each per `LOTUS_TESTING.md`, then delete the
 
 ## 🧩 Known Element Call iframe limitations (not fixable from our side)
 
-The in-call participant grid is rendered **inside EC's separate-origin iframe**,
-which we can style/place around but cannot inject UI into. Consequences from
-testing:
+> 🔱 **[EC-FORK]** These are the motivating issues for the **Element Call fork
+> initiative** — see [`HANDOFF_ELEMENT_CALL_FORK.md`](./HANDOFF_ELEMENT_CALL_FORK.md).
+> Once we build EC from our own source, A5/A6/A7 below become normal code fixes.
+> (Correction: the iframe is actually **same-origin** / self-hosted — we just
+> don't own EC's compiled source today.)
+
+The in-call participant grid is rendered **inside EC's iframe** (a pre-built npm
+bundle we don't own), which we can style/place around but cannot change the logic
+of. Consequences from testing:
 
 - **A5 — "Focus camera":** EC already supports native tile-pinning (click a video
   tile). Our bottom-bar "Focus camera" is a programmatic wrapper that clicks that