fix(tools/_lib): /etc/mosaic host-level fallback for credential resolution (#700)

packages/mosaic/framework/tools/git/detect-platform.sh

@@ -86,7 +86,16 @@ gitea_url_matches_host() {
 
 get_gitea_service_for_host() {
     local host="$1"
-    local cred_file="${MOSAIC_CREDENTIALS_FILE:-$HOME/.config/mosaic/credentials.json}"
+    local cred_file="${MOSAIC_CREDENTIALS_FILE:-}"
+    if [[ -z "$cred_file" ]]; then
+        # Same resolution chain as _lib/credentials.sh: profile HOME, then
+        # host-level /etc only if it exists; neither existing keeps the
+        # $HOME default (matches the lib's final := fallback).
+        cred_file="$HOME/.config/mosaic/credentials.json"
+        if [[ ! -f "$cred_file" && -f /etc/mosaic/credentials.json ]]; then
+            cred_file="/etc/mosaic/credentials.json"
+        fi
+    fi
 
     case "$host" in
         git.mosaicstack.dev)