Fix E2E select locator and add speed limit color mode

E2E fixes:
- Color mode select locator now uses option[value='highway'] filter
  instead of fragile page.locator("select").last()

Speed limit color mode:
- Extract maxspeed tags from BRouter tiledesc (with forward/backward
  direction handling following brouter-web's pattern)
- Color route and chart by speed limit: green ≤30, yellow ≤50,
  orange ≤70, red ≤100, dark red 100+ km/h
- Legend with speed thresholds, hover shows "X km/h"
- i18n: EN "Speed Limit" / DE "Tempolimit"
- Mock fixtures include maxspeed data

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

e2e/fixtures/brouter-mock.ts

@@ -40,6 +40,10 @@ const MOCK_ROUTE_3WP = {
     "residential", "residential", "cycleway", "cycleway", "path",
     "path", "tertiary", "tertiary", "residential", "residential",
   ],
+  maxspeeds: [
+    "30", "30", "unknown", "unknown", "unknown",
+    "unknown", "50", "50", "30", "30",
+  ],
 };
 
 /**
@@ -76,6 +80,9 @@ const MOCK_ROUTE_2WP = {
   highways: [
     "secondary", "secondary", "cycleway", "cycleway", "residential", "residential",
   ],
+  maxspeeds: [
+    "50", "50", "unknown", "unknown", "30", "30",
+  ],
 };
 
 /**