feat(e2e): add test mode infrastructure with BTERMINAL_TEST env isolation

Rust: watcher.rs/fs_watcher.rs skip watchers in test mode,
is_test_mode Tauri command. Frontend: wake-scheduler disable,
App.svelte test mode detection. AppConfig centralization in
bterminal-core (OnceLock pattern for path overrides).

v2/src-tauri/src/watcher.rs

@@ -37,6 +37,12 @@ impl FileWatcherManager {
         pane_id: &str,
         path: &str,
     ) -> Result<String, String> {
+        // In test mode, skip file watching to avoid inotify noise and flaky events
+        if std::env::var("BTERMINAL_TEST").map_or(false, |v| v == "1") {
+            return std::fs::read_to_string(path)
+                .map_err(|e| format!("Failed to read file: {e}"));
+        }
+
         let file_path = PathBuf::from(path);
         if !file_path.exists() {
             return Err(format!("File not found: {path}"));