fix(executor): isolate log files per task in parallel mode

Previously, all parallel tasks shared the same log file path, making it
difficult to debug individual task execution. This change creates a
separate log file for each task using the naming convention:
codeagent-wrapper-{pid}-{taskName}.log

Changes:
- Add withTaskLogger/taskLoggerFromContext for per-task logger injection
- Modify executeConcurrentWithContext to create independent Logger per task
- Update printTaskStart to display task-specific log paths
- Extract defaultRunCodexTaskFn for proper test hook reset
- Add runCodexTaskFn reset to resetTestHooks()

Test coverage: 93.7%

Generated with swe-agent-bot

Co-Authored-By: swe-agent-bot <agent@swe-agent.ai>

codeagent-wrapper/main_integration_test.go

@@ -426,10 +426,11 @@ ok-d`
 		t.Fatalf("expected startup banner in stderr, got:\n%s", stderrOut)
 	}
 
+	// After parallel log isolation fix, each task has its own log file
 	expectedLines := map[string]struct{}{
-		fmt.Sprintf("Task a: Log: %s", expectedLog): {},
-		fmt.Sprintf("Task b: Log: %s", expectedLog): {},
-		fmt.Sprintf("Task d: Log: %s", expectedLog): {},
+		fmt.Sprintf("Task a: Log: %s", filepath.Join(tempDir, fmt.Sprintf("codex-wrapper-%d-a.log", os.Getpid()))): {},
+		fmt.Sprintf("Task b: Log: %s", filepath.Join(tempDir, fmt.Sprintf("codex-wrapper-%d-b.log", os.Getpid()))): {},
+		fmt.Sprintf("Task d: Log: %s", filepath.Join(tempDir, fmt.Sprintf("codex-wrapper-%d-d.log", os.Getpid()))): {},
 	}
 
 	if len(taskLines) != len(expectedLines) {