✨ feat: add test suite, CI/CD pipeline, setup wizard, and upstream feature ports (#6)

Establish comprehensive quality infrastructure for a project that previously
had zero tests, enabling confident refactoring and community contributions
with automated guardrails. Port upstream enhancements for font normalization,
image element support, and arrow binding preservation.

🏗️ Testing infrastructure:
- Unit tests for SQLite persistence layer and element validation helpers
- Integration tests for REST API, WebSocket broadcast, and arrow binding
- E2E tests with Playwright for canvas rendering and real-time sync
- Vitest + Playwright configuration with proper isolation

👷 CI/CD pipeline:
- Auto-versioning from conventional commits on push to main
- Auto-publish to NPM and Docker Hub on GitHub release
- Matrix testing across Node 18/20/22 with pinned dependencies
- Docker health check with diagnostic logging on failure
- Preserve rollup status checks for branch protection gates

📦 Developer experience:
- Interactive setup wizard for first-time configuration
- Canvas clear confirmation and scene description tools
- Frontend helpers extracted for testability

🔧 Upstream feature ports:
- Font family normalization (string names to numeric IDs)
- Image element support with file management API
- Arrow binding preservation through server round-trips
- Vite config fix for font subsetting worker chunk names
- Idempotent database initialization for standalone Docker mode

🐛 Docker fixes:
- Set EXCALIDRAW_DB_PATH in both Dockerfiles to writable /app/data/
- Make initDb() idempotent and closeDb() reset-safe for test isolation

🎯 Provides the safety net needed for rapid iteration — every PR is
validated across 120 test cases before merge, and releases are fully
automated from commit to published package.

Co-authored-by: sanjibdevnathlabs <devnath.sanjib@gmail.com>

playwright.config.ts

@@ -0,0 +1,32 @@
+import { defineConfig, devices } from '@playwright/test';
+
+export default defineConfig({
+  testDir: './tests/e2e',
+  timeout: 30000,
+  expect: { timeout: 5000 },
+  fullyParallel: false,
+  retries: 0,
+  workers: 1,
+  reporter: 'list',
+  use: {
+    baseURL: 'http://localhost:3100',
+    trace: 'on-first-retry',
+  },
+  projects: [
+    {
+      name: 'chromium',
+      use: { ...devices['Desktop Chrome'] },
+    },
+  ],
+  webServer: {
+    command: 'node tests/e2e/start-server.js',
+    port: 3100,
+    timeout: 15000,
+    reuseExistingServer: !process.env.CI,
+    env: {
+      CANVAS_PORT: '3100',
+      HOST: 'localhost',
+      EXCALIDRAW_DB_PATH: '/tmp/excalidraw-e2e-test.db',
+    },
+  },
+});