feat(background-task): rendu live des tâches de fond — subscriber UI + canal IPC (#58)

Câble un canal attachable au flux de sortie d'une tâche de fond (runner
infrastructure + commande app-tauri + port/adaptateurs frontend) et le
panneau ProjectWorkStatePanel s'y abonne pour un rendu live au lieu d'un
état figé au dernier snapshot.

Validations obtenues avant commit :
- cargo test -p infrastructure --test background_task_runner : vert
- cargo check -p backend -p app-tauri : vert
- npx vitest run src/features/workstate/workstate.test.tsx : vert
- npm run typecheck : vert
- verdict QA #58 : vert

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

crates/infrastructure/src/background_task/runner.rs

@@ -101,6 +101,17 @@ impl CommandBackgroundRunner {
         u64::try_from(self.clock.now_millis().max(0)).unwrap_or(0)
     }
 
+    /// Returns the live PTY handle for a running task, when this runner still
+    /// owns one.
+    #[must_use]
+    pub fn pty_handle_for(&self, task_id: TaskId) -> Option<PtyHandle> {
+        self.running
+            .lock()
+            .expect("runner registry poisoned")
+            .get(&task_id)
+            .map(|control| control.pty_handle.clone())
+    }
+
     /// Detached worker driving one command to its single completion.
     #[allow(clippy::too_many_arguments)]
     async fn run_to_completion(

crates/infrastructure/src/lib.rs

@@ -25,6 +25,7 @@ pub mod id;
 pub mod input;
 pub mod inspector;
 pub mod issues;
+pub mod lock;
 pub mod mailbox;
 pub mod model_catalogue;
 pub mod model_server;
@@ -68,6 +69,7 @@ pub use inspector::{
     transcript_activity_token, ClaudeTranscriptInspector, ClaudeTranscriptTurnWatcher,
 };
 pub use issues::{FsIssueNumberAllocator, FsIssueStore};
+pub use lock::{acquire_app_data_dir_lock, AppDataDirLock, AppDataDirLockError};
 pub use mailbox::InMemoryMailbox;
 pub use model_catalogue::{
     EmbeddedCompatibilityMatrix, HttpProviderModelCatalogue, ProcessCliVersionReader,