feat: add /plugin docs page + TDP peripheral overhead

Plugin docs page (/plugin):
- Hero, feature grid, numbered install guide, screenshot gallery, install CTA
- Navbar 'Plugin' link added
- Screenshot slots with placeholders for 6 captures (flip HAS_SCREENSHOT
  once PNGs are dropped into /public/plugin/)
- Structured data (SoftwareApplication) + breadcrumbs

TDP fix:
- Add 3W fixed overhead to CPU+GPU power for screen/fan/speakers/peripherals
  so reported TDP is closer to total system power draw

apps/web/lib/routes.ts

@@ -19,6 +19,10 @@ export const routes = [
         title: "Devices",
         href: "/devices",
     },
+    {
+        title: "Plugin",
+        href: "/plugin",
+    },
     {
         title: "Contact",
         href: "/contact",