feat: Phase 4-5 — demo mode, polish, deploy, and bug fixes

Add demo mode with mock data provider, Docker deployment, Playwright
tests, PostHog analytics, error boundaries, and SEO metadata. Fix
residences API response unwrapping, kanban drag-and-drop with optimistic
updates, trailing slash proxy redirects, and column name mismatches with
Go API.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

src/components/shared/error-banner.tsx

@@ -9,8 +9,8 @@ interface ErrorBannerProps {
 
 export function ErrorBanner({ message = "Something went wrong. Please try again.", onRetry }: ErrorBannerProps) {
   return (
-    <div className="rounded-lg border border-destructive/50 bg-destructive/10 p-4 flex items-center gap-3">
-      <AlertTriangle className="size-5 text-destructive shrink-0" />
+    <div role="alert" aria-live="assertive" className="rounded-lg border border-destructive/50 bg-destructive/10 p-4 flex items-center gap-3">
+      <AlertTriangle className="size-5 text-destructive shrink-0" aria-hidden="true" />
       <p className="text-sm text-destructive flex-1">{message}</p>
       {onRetry && <Button variant="outline" size="sm" onClick={onRetry}>Retry</Button>}
     </div>