fix(caddy): evaluate {{env}} in env.js (templates mime)

Caddy `templates` only processes text/html + text/plain by default, so the
text/javascript env.js was served with {{env "API_BASE"}} unevaluated (a literal
that's also a JS parse error). Name the JS MIME types in the templates directive
so the API_BASE injection works — required for prod to point at the prod API
(staging worked only via the index.html fallback).

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

Caddyfile

@@ -14,9 +14,13 @@
 	}
 
 	# Runtime config: Caddy renders {{env "API_BASE"}} into env.js. Never cache it.
+	# `templates` only acts on text/html + text/plain by default, so JS responses
+	# are skipped unless their MIME type is named explicitly here.
 	handle /env.js {
-		templates
 		header Cache-Control "no-store"
+		templates {
+			mime text/javascript application/javascript
+		}
 		file_server
 	}