Release — suppress Windows git console windows (#6534) (#7115)

* fix: suppress console windows for git subprocess calls on Windows

On Windows, every git.exe spawned by the WebUI (update checks,
version detection, workspace git info, rollback inspection,
worktree management) creates a visible console window. When
Windows Terminal is the default terminal, each short-lived git
process opens a new tab. Combined with the 60-second version-skew
monitor polling /api/settings and the boot-time update check, this
produces a flood of flashing terminal tabs.

Root cause: subprocess.run() calls in api/updates.py, api/rollback.py,
api/worktrees.py, and api/workspace.py did not pass
creationflags=CREATE_NO_WINDOW on Windows. api/workspace_git.py
already had the fix (#5692); these four files were missed.

Backend fix:
- Add _windows_hide_flags() helper to each affected module
  (mirrors the existing pattern in api/workspace_git.py)
- Pass creationflags=_windows_hide_flags() to all git
  subprocess.run() calls (10 call sites across 4 files)

Frontend fix (prevent timeout->retry cascades):
- Increase update-check timeout from 30s/60s to 300s (5 min)
- Increase /api/settings fetches from 30s to 60s
- Increase /api/git-info fetch from 30s to 60s

The backend git fetch to GitHub can take 15s per repo; with both
WebUI and Agent repos checked sequentially plus other git calls,
the total easily exceeds the old 30s default frontend timeout,
triggering the api() wrapper auto-retry (3 attempts) and
amplifying the git process flood.

* [verified] fix: address Windows git subprocess review

---------

Co-authored-by: ya1yi2fa3 <ya1yi2fa3@users.noreply.github.com>
Co-authored-by: n <a@n>

api/subprocess_utils.py

@@ -0,0 +1,18 @@
+"""Dependency-light helpers for launching child processes consistently."""
+
+from __future__ import annotations
+
+import subprocess
+import sys
+
+
+def windows_hide_flags() -> int:
+    """Hide a short-lived console child on Win32 and remain a POSIX no-op.
+
+    ``CREATE_NO_WINDOW`` keeps captured stdout and stderr connected, unlike
+    detaching the process. Passing ``0`` elsewhere preserves the subprocess
+    default. See #5692.
+    """
+    if sys.platform == "win32":
+        return getattr(subprocess, "CREATE_NO_WINDOW", 0)
+    return 0