fix(oracle-l8): close 3 polish caveats (dispatch labels / chat unread / leftrail leak)

Oracle PASS-with-caveats; closing all 3:

1. Wizard dispatch labels were 'human'/'agent'/'system' (impl-ish).
   Now 'Person'/'Assistant'/'System' in both the dropdown and the
   preview-pane badge.

2. Chat badge was thread COUNT (a buyer with 5 chats sees '5' forever).
   Now real unread count, computed locally from localStorage heads +
   read maps that the Chat scene already persists. App.tsx topbar
   poll still only fires 2 network calls (listThreads + workItems);
   per-thread unread math is zero-network.

3. LeftRail toast leaked 'POST /api/runtime/transactions/{id}/actions/
   submit' / save_draft. Rewritten as 'Switch to live mode and sign
   in to submit this action against EA2.'

Plus engineering-string sweep elsewhere: 'demo.flow-master.ai' /
'bundled JSON' / 'in-browser fetch' references removed from:
- App.tsx mode toggle title
- MissionControl loading spinner
- Landing mode-button title
- state/store snapshot toast
- data/live.ts + data/synthetic.ts tour-step bodies
- buildScenarios.ts tagline

Source-grep confirms no remaining user-visible engineering jargon
referencing the backend hostname or raw endpoints.

src/lib/buildScenarios.ts

@@ -176,7 +176,7 @@ function buildScenarioFromGraph(
     defName: pd.display_name || pd.name,
     version: versionLabel,
     headlineTx: headlineRt?.transaction_id ?? null,
-    tagline: `${pd.display_name || pd.name} · ${versionLabel} · live from demo.flow-master.ai`,
+    tagline: `${pd.display_name || pd.name} · ${versionLabel} · live from EA2`,
     steps,
     edges,
     rules,