feat: initial Greasy Sprocket website — Astro static + Go feedback service

- Astro 5.x static site with content collections for extensions
- Pages: index, [slug] (per-extension), coffee (Ko-fi), feedback form
- Go binary gs-feedback: SQLite storage + Discord webhook notification
- Nginx config: static serving + POST proxy to Go backend
- Deploy script: build + rsync to VPS
- ThockBoard landing page with features and sound pack listing

astro/public/favicon.svg

@@ -0,0 +1,9 @@
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+  <rect width="128" height="128" rx="28" fill="#0c0a09"/>
+  <circle cx="64" cy="64" r="36" fill="none" stroke="#f97316" stroke-width="6"/>
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+</svg>