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/config.py

@@ -0,0 +1,13 @@
+import os
+
+# Base URL of the CYD ThermoPro Bridge.
+CYD_BASE_URL = os.environ.get("CYD_BASE_URL", "http://192.168.2.55")
+
+# How often (seconds) the backend polls the CYD for new readings.
+POLL_INTERVAL = int(os.environ.get("POLL_INTERVAL", "5"))
+
+# SQLite database path.
+DATABASE_PATH = os.environ.get("DATABASE_PATH", "thermopro.db")
+
+# Number of minutes of history shown by default on the dashboard chart.
+DEFAULT_CHART_MINUTES = int(os.environ.get("DEFAULT_CHART_MINUTES", "60"))