fix(windows): suppress console window flash on subprocess spawns

Add creationflags=CREATE_NO_WINDOW to every Windows Popen call
across the terminal, process registry, code execution, and kanban
worker subsystems. Prevents visible CMD windows from flashing on
the user's desktop during agent operation.

Also adds the _IS_WINDOWS module constant to kanban_db.py where
it was missing, for consistency with the other patched files.

5 Popen sites across 4 files:
- tools/environments/local.py (terminal foreground spawn)
- tools/process_registry.py (background process spawn)
- tools/code_execution_tool.py (sandbox + interpreter probe)
- hermes_cli/kanban_db.py (kanban worker spawn)

hermes_cli/kanban_db.py

@@ -93,6 +93,7 @@ from toolsets import get_toolset_names
 VALID_STATUSES = {"triage", "todo", "ready", "running", "blocked", "done", "archived"}
 VALID_WORKSPACE_KINDS = {"scratch", "worktree", "dir"}
 KNOWN_TOOLSET_NAMES = frozenset(name.casefold() for name in get_toolset_names())
+_IS_WINDOWS = sys.platform == "win32"
 
 # A running task's claim is valid for 15 minutes; after that the next
 # dispatcher tick reclaims it.  Workers that outlive this window should call
@@ -4024,6 +4025,7 @@ def _default_spawn(
             stderr=subprocess.STDOUT,
             env=env,
             start_new_session=True,
+            creationflags=subprocess.CREATE_NO_WINDOW if _IS_WINDOWS else 0,
         )
     except FileNotFoundError:
         log_f.close()

tools/code_execution_tool.py

@@ -1238,6 +1238,7 @@ def execute_code(
             stderr=subprocess.PIPE,
             stdin=subprocess.DEVNULL,
             preexec_fn=None if _IS_WINDOWS else os.setsid,
+            creationflags=subprocess.CREATE_NO_WINDOW if _IS_WINDOWS else 0,
         )
 
         # --- Poll loop: watch for exit, timeout, and interrupt ---
@@ -1568,6 +1569,7 @@ def _is_usable_python(python_path: str) -> bool:
              "import sys; sys.exit(0 if sys.version_info >= (3, 8) else 1)"],
             timeout=5,
             capture_output=True,
+            creationflags=subprocess.CREATE_NO_WINDOW if _IS_WINDOWS else 0,
         )
         return result.returncode == 0
     except (OSError, subprocess.TimeoutExpired, subprocess.SubprocessError):

tools/environments/local.py

@@ -513,6 +513,7 @@ class LocalEnvironment(BaseEnvironment):
             stderr=subprocess.STDOUT,
             stdin=subprocess.PIPE if stdin_data is not None else subprocess.DEVNULL,
             preexec_fn=None if _IS_WINDOWS else os.setsid,
+            creationflags=subprocess.CREATE_NO_WINDOW if _IS_WINDOWS else 0,
             cwd=_popen_cwd,
         )
         if not _IS_WINDOWS:

tools/process_registry.py

@@ -557,6 +557,7 @@ class ProcessRegistry:
             stderr=subprocess.STDOUT,
             stdin=subprocess.PIPE,
             preexec_fn=None if _IS_WINDOWS else os.setsid,
+            creationflags=subprocess.CREATE_NO_WINDOW if _IS_WINDOWS else 0,
         )
 
         session.process = proc