Fix /metrics double-gzip + deploy script for amd64 build

The Echo gzip middleware was wrapping promhttp's pre-gzipped output, so
vmagent received double-compressed bytes that failed the Prometheus
parser with binary garbage. Skipping /metrics in the gzip Skipper.

Three deploy-script fixes uncovered while shipping this:
- _config.sh had backticks around \"kubectl get cm\" inside the python
  heredoc, which bash treated as command substitution when KUBECONFIG
  was set. Quoted the literal instead.
- 03-deploy.sh now passes --platform linux/amd64 to all docker builds
  so arm64 Macs don't push images that fail with \"exec format error\"
  on the Hetzner CX nodes.
- OBS_INGEST_TOKEN lookup was reading deploy-k3s/prod.env instead of
  the actual deploy/prod.env at the repo root.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

internal/router/router.go

@@ -107,11 +107,14 @@ func SetupRouter(deps *Dependencies) *echo.Echo {
 	e.Use(corsMiddleware(cfg))
 	e.Use(i18n.Middleware())
 
-	// Gzip compression (skip media endpoints since they serve binary files)
+	// Gzip compression (skip media endpoints since they serve binary files;
+	// also skip /metrics because promhttp does its own content negotiation,
+	// so wrapping it here produces double-gzipped output that breaks scrapers).
 	e.Use(middleware.GzipWithConfig(middleware.GzipConfig{
 		Level: 5,
 		Skipper: func(c echo.Context) bool {
-			return strings.HasPrefix(c.Request().URL.Path, "/api/media/")
+			path := c.Request().URL.Path
+			return strings.HasPrefix(path, "/api/media/") || path == "/metrics"
 		},
 	}))