feat: PWA support with hockey puck icon

Adds full PWA compliance: web app manifest, service worker with
cache-first static / network-first scoreboard strategy, and a
generated hockey puck icon (512, 192, 180, 32px) on the app's
dark navy background. Includes all required meta tags for iOS
standalone mode and a /favicon.ico route.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

app/routes.py

@@ -1,12 +1,32 @@
 import json
 
-from flask import render_template, jsonify
+from flask import render_template, jsonify, send_from_directory
 
 from app import app
 from app.config import SCOREBOARD_DATA_FILE
 from app.games import parse_games
 
 
+@app.route("/manifest.json")
+def manifest():
+    return send_from_directory(app.static_folder, "manifest.json")
+
+
+@app.route("/sw.js")
+def service_worker():
+    response = send_from_directory(app.static_folder, "sw.js")
+    response.headers["Service-Worker-Allowed"] = "/"
+    response.headers["Cache-Control"] = "no-cache"
+    return response
+
+
+@app.route("/favicon.ico")
+def favicon():
+    return send_from_directory(
+        app.static_folder, "icon-32x32.png", mimetype="image/png"
+    )
+
+
 @app.route("/")
 def index():
     return render_template("index.html")