ci: adopt gobject-linter as a blocking static-analysis gate

Add gobject-linter (github.com/bilelmoussaoui/gobject-linter) to CI to catch
GObject/GLib correctness and idiom issues.

Config (gobject-linter.toml):
- min_glib_version = 2.80 (libadwaita >= 1.8)
- default_level = error: every enabled rule blocks CI
- type_style ignored: the project deliberately uses plain C scalar types
- untranslated_string ignored: app is not internationalized yet
- use_auto_cleanup downgraded to warn: it mis-fires on floating GVariant
  references (consumed by g_variant_new_tuple/builders) and on objects kept
  alive past the function (the GlobalShortcuts GDBusProxy); converting those to
  g_autoptr would over-unref and crash, so it advises rather than blocks

Workflow (.github/workflows/gobject-linter.yml): runs the official container
image on push/PR, uploads SARIF to code scanning (non-fatal for fork PRs), and
fails the build on any error-level finding.

Code is brought to a green baseline by applying the auto-fixable findings:
- strcmp -> g_strcmp0 (NULL-safe)
- manual g_free/g_strdup -> g_set_str
- manual source removal -> g_clear_handle_id / g_clear_object / g_clear_pointer
- g_string_free(.., FALSE) -> g_string_free_and_steal
- g_idle_add one-shot -> g_idle_add_once (id now stored and cleared in finalize,
  also closing a latent use-after-free if the window is finalized first)
- include ordering and #pragma once

The 37 remaining use_auto_cleanup findings are reported as warnings for
incremental manual review.

1 files changed, 2 insertions, 1 deletions

diff --git a/src/gsr-config-page.h b/src/gsr-config-page.h
index 851bd76..bf5304b 100644
--- a/src/gsr-config-page.h
+++ b/src/gsr-config-page.h
@@ -1,8 +1,9 @@
 #pragma once
 
 #include <adwaita.h>
-#include "gsr-info.h"
+
 #include "gsr-config.h"
+#include "gsr-info.h"
 
 G_BEGIN_DECLS