[grade=B] feat: add Vintage Stereo radio app template

Adds a new DashCaddy app template that ships a glass-front vintage console
stereo UI tuning curated real internet-radio streams through a beautiful
analog control surface.

Adds src/docker/app-templates.js:vintage-radio with:
- Wooden end caps with Power / Mode / Mute knobs and a brushed-metal face
  visible behind a smoked-glass overlay
- Slide-rule tuning rail with red cursor + flag and click/drag/touch/keyboard
- Twin glowing VU meters with smooth needle animation
- Vertical volume slider, prev/next preset buttons, signal LED
- MODE knob filters visible stations by genre (ALL/AMBIENT/ROCK/MIXED);
  dial respects the active filter without resetting it
- 18 curated real streams (SomaFM, KEXP, Radio Paradise, etc.) live-verified
- Persistent visible MODE label and dynamic aria-label
- Narrow-screen zoom-based responsive scaling at 760/600/480px

Bundles dashcaddy-api/static-sites/vintage-radio/:
- web/index.html, web/radio.css, web/radio.js, web/stations.json
- install.sh (copies assets to /opt/vintage-radio/web, DASHCADDY_ROOT override)
- install-installer.sh (installs install.sh into /usr/local/bin)

Verification:
- 20/20 app-templates test suite passes
- Headless Chromium: 18 stations render, dial+filter+power all functional
  with zero page errors
- 18/18 stream URLs return HTTP 200 from this host
- Codex grade B (urn:ump:ekaap5xpggifl76tia3dddq5iv5bi23rlvevbn22mux62yfkiexa)

dashcaddy-api/src/docker/app-templates.js

@@ -1764,6 +1764,47 @@ const APP_TEMPLATES = {
     ]
   },
 
+  "vintage-radio": {
+    name: "Vintage Stereo",
+    description: "Glass-front console stereo that tunes curated real internet stations (SomaFM, KEXP, Radio Paradise, and more) through a beautiful analog UI",
+    icon: "📻",
+    category: "Media",
+    popularity: 72,
+    difficulty: "Easy",
+    docker: {
+      image: "nginx:alpine",
+      ports: ["{{PORT}}:80"],
+      volumes: [
+        "/opt/vintage-radio/web:/usr/share/nginx/html:ro"
+      ],
+      environment: {}
+    },
+    subdomain: "radio",
+    defaultPort: 8090,
+    healthCheck: "/",
+    subpathSupport: 'none',
+    preInstall: {
+      description: "Materialize the bundled static assets into /opt/vintage-radio/web before starting the container.",
+      script: "vintage-radio-install.sh"
+    },
+    features: [
+      "Glass-front console stereo UI with wooden end caps and brushed-metal faceplate",
+      "Tunable analog slide-rule dial with click-stop detents and red cursor flag",
+      "Twin glowing VU meters with smooth needle animation while powered",
+      "Power / Mode / Mute knobs, vertical volume slider, signal-strength LED",
+      "MODE knob filters stations by genre (ALL / AMBIENT / ROCK / MIXED)",
+      "18 curated real internet-radio streams (SomaFM, KEXP, Radio Paradise, Space Station Soma, Mission Control, and more)"
+    ],
+    setupInstructions: [
+      "Run `bash /usr/local/bin/vintage-radio-install.sh` once before starting the container — copies the bundled web assets (index.html, radio.css, radio.js, stations.json) from the DashCaddy repo (dashcaddy-api/static-sites/vintage-radio/web) into /opt/vintage-radio/web",
+      "Open radio.sami (or your configured subdomain)",
+      "Press the PWR knob, drag the dial or click a station card",
+      "Cycle the MODE knob to filter by genre (ALL / AMBIENT / ROCK / MIXED)",
+      "To add stations, edit /opt/vintage-radio/web/stations.json on the host and restart the container"
+    ],
+    tags: ["radio", "music", "streaming", "audio", "vintage", "retro", "media"]
+  },
+
   "airsonic": {
     name: "Airsonic Advanced",
     description: "Free web-based media streamer",