Add skip_tests/skip_builds flags, fix build-stage failures

1. dry-run.yml: Add skip_tests and skip_builds workflow_dispatch inputs
   for faster iteration. Build jobs use always() to run even when tests
   are skipped.

2. Windows archive: Switch from PowerShell Copy-Item to MSYS2 shell
   with .exe extension detection. MSYS2 Clang produces .exe suffix
   that Copy-Item didn't account for.

3. Linux embed: Use absolute path for ld output when cd'd into dist
   directory. Relative path build/c/embedded/*.o was invalid from
   inside graph-ui/dist/.

4. release.yml: Same Windows archive fix as dry-run.

scripts/embed-frontend.sh

@@ -85,7 +85,8 @@ for file in "${FILES[@]}"; do
         rm -f "$local_c"
     else
         # Linux: ld -r -b binary (zero bloat)
-        (cd "$DIST_DIR" && ld -r -b binary -o "$obj" "$rel")
+        abs_obj="$(cd "$(dirname "$0")/.." && pwd)/$obj"
+        (cd "$DIST_DIR" && ld -r -b binary -o "$abs_obj" "$rel")
     fi
 
     OBJ_FILES+=("$obj")