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>

tests/residences.spec.ts

@@ -0,0 +1,21 @@
+import { test, expect } from "@playwright/test";
+
+test.describe("Residences (Demo Mode)", () => {
+  test.beforeEach(async ({ page }) => {
+    await page.goto("/demo/app/residences");
+  });
+
+  test("displays residence list", async ({ page }) => {
+    await expect(page.locator("h1, h2").first()).toContainText(/residences|properties/i);
+  });
+
+  test("navigate to add residence", async ({ page }) => {
+    await page.click("text=Add Residence");
+    await expect(page).toHaveURL("/demo/app/residences/new");
+  });
+
+  test("add residence form has required fields", async ({ page }) => {
+    await page.goto("/demo/app/residences/new");
+    await expect(page.locator('input[name="name"], input[name="title"]').first()).toBeVisible();
+  });
+});