feat: separate create/edit form pages, Playwright test infrastructure, /auth/token endpoint

Move all CRUD create/edit forms from inline on list pages to dedicated form pages
with back-button navigation and post-save redirect. Add Playwright Docker container
(browser server on port 3000) with 25 passing E2E tests covering login, navigation,
and site CRUD workflows. Add POST /auth/token endpoint for clean JWT retrieval.

infra/tools/playwright_smoke.py

@@ -0,0 +1,46 @@
+#!/usr/bin/env python3
+"""Quick smoke test: verify Playwright can reach the Central UI through Traefik."""
+
+import sys
+from playwright.sync_api import sync_playwright
+
+# The browser runs inside Docker, so use the Docker network hostname for Traefik.
+# The Playwright server WebSocket is exposed to the host on port 3000.
+TRAEFIK_URL = "http://scadalink-traefik"
+PLAYWRIGHT_WS = "ws://localhost:3000"
+
+
+def main():
+    with sync_playwright() as p:
+        print(f"Connecting to Playwright server at {PLAYWRIGHT_WS} ...")
+        browser = p.chromium.connect(PLAYWRIGHT_WS)
+
+        page = browser.new_page()
+        print(f"Navigating to {TRAEFIK_URL} ...")
+        response = page.goto(TRAEFIK_URL, wait_until="networkidle", timeout=15000)
+
+        status = response.status if response else None
+        title = page.title()
+        url = page.url
+
+        print(f"  Status: {status}")
+        print(f"  Title:  {title}")
+        print(f"  URL:    {url}")
+
+        # Check for the login page (unauthenticated users get redirected)
+        has_login = page.locator("input[type='password'], form[action*='login'], button:has-text('Login'), button:has-text('Sign in')").count() > 0
+        if has_login:
+            print("  Login form detected: YES")
+
+        browser.close()
+
+        if status and 200 <= status < 400:
+            print("\nSMOKE TEST PASSED: Central UI is reachable through Traefik.")
+            return 0
+        else:
+            print(f"\nSMOKE TEST FAILED: unexpected status {status}")
+            return 1
+
+
+if __name__ == "__main__":
+    sys.exit(main())