feat: add Go module proxy (GOPROXY protocol) (#59)

* feat: add Go module proxy (GOPROXY protocol) (#47)

Implements caching proxy for Go modules with 5 standard endpoints:
- GET /go/{module}/@v/list — list versions
- GET /go/{module}/@v/{version}.info — version metadata
- GET /go/{module}/@v/{version}.mod — go.mod file
- GET /go/{module}/@v/{version}.zip — module zip
- GET /go/{module}/@latest — latest version info

Features:
- Module path encoding/decoding per Go spec (!x → X)
- Immutable caching (.info/.mod/.zip never overwritten)
- Mutable endpoints (@v/list, @latest) refreshed from upstream
- Configurable upstream (default: proxy.golang.org)
- Separate timeout for .zip downloads (default: 120s)
- Size limit for zips (default: 100MB)
- Path traversal protection
- Dashboard integration (stats, mount points, index)
- 25 unit tests (encoding, path splitting, safety, content-type)

Closes #47

* style: cargo fmt

* feat(ui): add Go pages, compact cards, fix icons

- Go in sidebar + list/detail pages with go get command
- Dashboard: fix fallback icon (was Docker whale for Go)
- Compact registry cards: lg:grid-cols-6, all 6 in one row
- Cargo icon: crate boxes instead of truck
- Go icon: stylized Go text (sidebar + dashboard)

* fix(go): URL-decode path + send encoded paths to upstream

Go client sends %21 for ! in module paths. Axum wildcard does not
auto-decode, so we percent-decode manually. Upstream proxy.golang.org
expects encoded paths (with !), not decoded uppercase.

Tested: full Pusk build (22 modules, 135MB cached) including
SherClockHolmes/webpush-go with triple uppercase encoding.

* style: cargo fmt

nora-registry/src/main.rs

@@ -326,7 +326,8 @@ async fn run_server(config: Config, storage: Storage) {
         .merge(registry::npm_routes())
         .merge(registry::cargo_routes())
         .merge(registry::pypi_routes())
-        .merge(registry::raw_routes());
+        .merge(registry::raw_routes())
+        .merge(registry::go_routes());
 
     // Routes WITHOUT rate limiting (health, metrics, UI)
     let public_routes = Router::new()