fix(prod): stop garbage page from double Content-Encoding header

On this non-FastCGI host Grav's shutdown early-connection-close can't
fastcgi_finish_request(), so it emits 'Content-Encoding: identity' to ask
the webserver not to compress — but Apache mod_deflate compresses anyway
and adds 'Content-Encoding: gzip'. Two conflicting headers => browsers
render raw gzip bytes (garbage page). Surfaced when prod flipped to
debug:false today (activated Grav's full output path).

Fix in the prod env override: debugger.shutdown.close_connection:false
skips the identity-header path so mod_deflate compresses cleanly (single
header). Verified: one 'content-encoding: gzip', page renders correctly.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01Np4cMQLF77i664CAQXySzU

deploy/env/prod/system.yaml

@@ -18,3 +18,21 @@ twig:
   cache: true
   debug: false
   auto_reload: false
+
+# Compression / connection handling.
+#
+# This host is not FastCGI (no fastcgi_finish_request()), so Grav's shutdown
+# "early connection close" falls back to emitting `Content-Encoding: identity`
+# to ask the webserver not to compress. But Apache's mod_deflate compresses
+# anyway and adds `Content-Encoding: gzip`, giving TWO conflicting headers —
+# the browser can't decode the body and renders raw gzip bytes (a garbage
+# page). Note: allow_webserver_gzip:true takes the SAME identity branch, so it
+# does not help. The real fix is to disable the early-close path, so Grav never
+# emits the bogus header and mod_deflate compresses cleanly (single header).
+debugger:
+  shutdown:
+    close_connection: false
+# Let the webserver own gzip; Grav does not compress or double-label.
+cache:
+  gzip: false
+  allow_webserver_gzip: false