Fix lint issues and improve test suite resilience

- compose.matrix.yml: add trailing newline
- compose.ftp-222*.yml: fix YAML indentation (8->6 spaces)
- entrypoint.sh.tmpl: fix SC2198 ([ -n "$@" ] -> [ $# -gt 0 ])
- All .tmpl files: migrate from {{ env }} to {{ getenv }} for gomplate v5 compat
- uploads.ini.tmpl: add {{- / -}} whitespace trimming, fix double-space typo
- tests/run.sh: only run ShellCheck on *.sh.tmpl files
- tests/test_shell.sh: gracefully skip if shellcheck not installed
- tests/test_templates.sh: remove dead render() function,
  gracefully skip if gomplate not found, use set -a/. for env sourcing
- tests/test_compose_config.sh: validate override files combined
  with compose.yml, skip partial snippets needing more context
- README.md: add test instructions with brew install

uploads.ini.tmpl

@@ -1,10 +1,10 @@
-{{ $upload_max_size := "256M" }}
-{{ if ne (env "UPLOAD_MAX_SIZE") "" }} {{ $upload_max_size = env "UPLOAD_MAX_SIZE" }} {{ end }}
-{{ $upload_max_time := "30" }}
-{{ if ne (env "UPLOAD_MAX_TIME") "" }} {{ $upload_max_time = env "UPLOAD_MAX_TIME" }} {{ end }}
+{{- $upload_max_size := "256M" -}}
+{{- if ne (getenv "UPLOAD_MAX_SIZE") "" }}{{ $upload_max_size = getenv "UPLOAD_MAX_SIZE" }}{{ end -}}
+{{- $upload_max_time := "30" -}}
+{{- if ne (getenv "UPLOAD_MAX_TIME") "" }}{{ $upload_max_time = getenv "UPLOAD_MAX_TIME" }}{{ end -}}
 
 file_uploads = On
-upload_max_filesize =  {{ $upload_max_size }}
+upload_max_filesize = {{ $upload_max_size }}
 post_max_size = {{ $upload_max_size }}
 memory_limit = {{ $upload_max_size }}
 max_execution_time = {{ $upload_max_time }}