feat: add PWA frontend for CYD ThermoPro dashboard

Add a Flask backend + SQLite + HTML/CSS/JS PWA that:
- Polls the CYD /api/latest endpoint
- Stores readings, sessions, and freeform notes in SQLite
- Displays probe cards with target setpoints and preset options
- Renders temperature history with Chart.js
- Serves a PWA manifest and dark-themed dashboard

Also update cyd-bridge/README.md with verified bringup instructions.

frontend/static/manifest.json

@@ -0,0 +1,20 @@
+{
+  "name": "ThermoPro CYD Dashboard",
+  "short_name": "CYD BBQ",
+  "start_url": "/",
+  "display": "standalone",
+  "background_color": "#1a1a1a",
+  "theme_color": "#ff6b35",
+  "icons": [
+    {
+      "src": "icon-192.png",
+      "sizes": "192x192",
+      "type": "image/png"
+    },
+    {
+      "src": "icon-512.png",
+      "sizes": "512x512",
+      "type": "image/png"
+    }
+  ]
+}