refactor: replace !!origin proxy with dedicated isApiMode in review editor

[backnotprop]

Problem

The review editor uses !!origin as a proxy for "is there a server backing this UI?" in multiple places:

• useCodeAnnotationDraft({ isApiMode: !!origin, ... }) (line 175)
• useExternalAnnotations({ enabled: !!origin }) (line 189)
• if (!origin) return; // Demo mode in the keyboard shortcut handler (line 954)
• Conditional UI rendering ({origin ? ( at line 1102)

origin is an identity field ("claude-code", "opencode", "pi") indicating who launched the review. It's not a connectivity signal. The standalone dev server (apps/review/) doesn't set origin, so all server-dependent features are silently disabled there.

Proposed Fix

Add a dedicated isApiMode boolean state to ReviewApp, matching the pattern already used in the plan editor (packages/editor/App.tsx):

const [isApiMode, setIsApiMode] = useState(false);

Set it in the /api/diff fetch:

• .then(...) → setIsApiMode(true)
• .catch(...) → remains false

Replace all !!origin API-mode checks with isApiMode. Leave origin for its intended purpose: display branding and agent-specific features.

Files

• packages/review-editor/App.tsx — main change
• packages/ui/hooks/useCodeAnnotationDraft.ts — already accepts isApiMode param, just needs the correct value passed in