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

tests/test_templates.sh

@@ -11,27 +11,20 @@ gomplate="${GOMPLATE_BIN:-gomplate}"
 # Ensure gomplate is installed before running template tests
 require_gomplate() {
     if ! command -v "$gomplate" &>/dev/null; then
-        echo "gomplate not found. Install it from https://github.com/hairyhenderson/gomplate"
-        echo "or set GOMPLATE_BIN env var."
-        exit 1
+        echo "  SKIP  gomplate not found (install from https://github.com/hairyhenderson/gomplate or set GOMPLATE_BIN)"
+        exit 0
     fi
 }
 
-render() {
-    local tmpl=$1 envfile=$2
-    "$gomplate" \
-        --template t="$tmpl" \
-        --context "_=fmt:%s" \
-        --datasource "env=env://?$envfile" \
-        -f "$tmpl" 2>/dev/null
-}
-
 # Render a template by exporting env vars directly
 # This avoids gomplate datasource quirks with .env files
 render_via_env() {
     local tmpl=$1 envfile=$2
-    # shellcheck disable=2046
-    env $(xargs < "$envfile") "$gomplate" -f "$tmpl" 2>/dev/null
+    set -a
+    # shellcheck disable=1090,1091
+    . "$envfile"
+    set +a
+    "$gomplate" -f "$tmpl" 2>/dev/null
 }
 
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