test(dashboard): serve vendored assets in the playwright route harness

The three playwright dashboard suites intercept every request with
page.route("**/*") and fall through to route.continue_() for anything they do
not recognise. While the templates pointed at unpkg.com and cdn.tailwindcss.com
those fall-throughs were absolute URLs that CI fetched over the real network,
so Alpine loaded by accident. Now that the assets are relative they resolve
against the harness's fake origin (127.0.0.1:8788, headroom.local), where
nothing is listening: Alpine never loads, every `<template x-if>` under <main>
renders nothing, and the tests that expect content fail while the ones that
expect an empty state pass vacuously.

Serve /dashboard/static/* from STATIC_DIR in the harness. The suites no longer
depend on outbound network access to a public CDN.

tests/test_dashboard_cache_lifetime_playwright.py

@@ -17,7 +17,11 @@ from urllib.parse import urlsplit
 import pytest
 
 from headroom.dashboard import get_dashboard_html
-from tests.test_dashboard_cache_ttl_playwright import _sample_history, _sample_stats
+from tests.test_dashboard_cache_ttl_playwright import (
+    _fulfill_static_asset,
+    _sample_history,
+    _sample_stats,
+)
 
 playwright = pytest.importorskip("playwright.sync_api")
 Page = playwright.Page
@@ -52,6 +56,8 @@ def _install_dashboard_routes(page: Page, stats: dict) -> None:
         if path in ("/dashboard", "/"):
             route.fulfill(status=200, content_type="text/html", body=dashboard_html)
             return
+        if _fulfill_static_asset(route, path):
+            return
         if "/stats-history" in path:
             route.fulfill(status=200, content_type="application/json", body=json.dumps(history))
             return

tests/test_dashboard_cache_net_playwright.py

@@ -18,7 +18,11 @@ from urllib.parse import urlsplit
 import pytest
 
 from headroom.dashboard import get_dashboard_html
-from tests.test_dashboard_cache_ttl_playwright import _sample_history, _sample_stats
+from tests.test_dashboard_cache_ttl_playwright import (
+    _fulfill_static_asset,
+    _sample_history,
+    _sample_stats,
+)
 
 playwright = pytest.importorskip("playwright.sync_api")
 Page = playwright.Page
@@ -56,6 +60,8 @@ def _install_dashboard_routes(page: Page, stats: dict) -> None:
         if path in ("/dashboard", "/"):
             route.fulfill(status=200, content_type="text/html", body=dashboard_html)
             return
+        if _fulfill_static_asset(route, path):
+            return
         if "/stats-history" in path:
             route.fulfill(status=200, content_type="application/json", body=json.dumps(history))
             return

tests/test_dashboard_cache_ttl_playwright.py

@@ -9,7 +9,7 @@ from urllib.parse import urlsplit
 
 import pytest
 
-from headroom.dashboard import get_dashboard_html
+from headroom.dashboard import STATIC_DIR, get_dashboard_html
 
 playwright = pytest.importorskip("playwright.sync_api")
 Page = playwright.Page
@@ -153,6 +153,25 @@ def _sample_history() -> dict:
     }
 
 
+def _fulfill_static_asset(route, path: str) -> bool:  # type: ignore[no-untyped-def]
+    """Serve the vendored dashboard JS from disk; True when it handled the route.
+
+    The harnesses in this file and its siblings intercept every request, so the
+    dashboard's relative asset URLs would otherwise fall through to a real fetch
+    against a fake origin with nothing listening. Alpine has to load: every
+    section of <main> lives inside a `<template x-if>`, which renders nothing at
+    all without it, so an empty <main> is the symptom to look for here.
+    """
+    if not path.startswith("/dashboard/static/"):
+        return False
+    route.fulfill(
+        status=200,
+        content_type="text/javascript",
+        body=(STATIC_DIR / Path(path).name).read_bytes(),
+    )
+    return True
+
+
 def _install_dashboard_routes(page: Page) -> None:
     stats = _sample_stats()
     history = _sample_history()
@@ -167,6 +186,8 @@ def _install_dashboard_routes(page: Page) -> None:
         if path in ("/dashboard", "/"):
             route.fulfill(status=200, content_type="text/html", body=dashboard_html)
             return
+        if _fulfill_static_asset(route, path):
+            return
         if "/stats-history" in path:
             route.fulfill(
                 status=200,