docs: update stale tabs.js→swarm.js/call.js references

After the SW4RM and Y3R C4LL extractions from tabs.js (PRs merged
earlier), several docs still pointed at `assets/tabs.js::fn`. Update
them to the authoritative module:

- dashboard.md: renderContainers, buildAgentTree → swarm.js
                renderApprovals → call.js
                renderPeerHives → swarm.js
- shape.md: generic "tabs.js render function" → "domain module"
- conventions.md: clarify async-form listener lives in tabs.js (dashboard)
                  AND app.js (per-agent UI)

docs/web-ui/shape.md

@@ -187,7 +187,7 @@ listener: read `data-confirm`, swap the button to a spinner, POST
 re-render), call `refreshState()`. State shapes live in
 `dashboard.rs::StateSnapshot` and `web_ui.rs::StateSnapshot` — when
 adding state fields, plumb through the snapshot struct and the
-relevant `assets/tabs.js` render function.
+relevant domain module (`assets/swarm.js`, `assets/call.js`, etc.) render function.
 
 **Focus preservation:** `refreshState` checks whether
 `document.activeElement` sits inside one of the managed sections