US-005: Typed task packet format with TaskScope enum

- Add TaskScope enum with Workspace, Module, SingleFile, Custom variants
- Update TaskPacket struct with scope_path and worktree fields
- Add validation for scope-specific requirements
- Fix tests in task_packet.rs, task_registry.rs, and tools/src/lib.rs
- Export TaskScope from runtime crate

Closes US-005 (Phase 4)

rust/crates/tools/src/lib.rs

@@ -9554,9 +9554,12 @@ printf 'pwsh:%s' "$1"
 
     #[test]
     fn run_task_packet_creates_packet_backed_task() {
+        use runtime::task_packet::TaskScope;
         let result = run_task_packet(TaskPacket {
             objective: "Ship packetized runtime task".to_string(),
-            scope: "runtime/task system".to_string(),
+            scope: TaskScope::Module,
+            scope_path: Some("runtime/task system".to_string()),
+            worktree: Some("/tmp/wt-packet".to_string()),
             repo: "claw-code-parity".to_string(),
             branch_policy: "origin/main only".to_string(),
             acceptance_tests: vec![