Add vim list nav, fix window-title padding toggle, widen title spacing

TUI:
- VimListView: j/k now move down/up in the project and session lists
  (arrow keys still work); used by both list widgets.

tmux status bar:
- Widen the gap between window cells via a 2-space window-status-separator
  (WINDOW_STATUS_SEPARATOR).
- Fix the current-window cell toggling between padded " 1: name " and
  unpadded "1: name". The per-window status format is static, but
  set_window_label re-asserted it on every 3s poll — letting a competing
  writer (e.g. a stale TUI process running older code with a differently
  padded format) flip the cell each cycle. The format is now owned by a
  single write-once path (new_window at creation, apply_theme for existing
  windows); the poll updates only the dynamic @hqt_label.

Also lands pre-staged scaffolding: AGENTS.md quality gate, TODO.md backlog,
and ty dev dependency.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

tests/test_tmux.py

@@ -784,21 +784,25 @@ async def test_poll_info_rc_nonzero_all_dead(runner):
 
 
 @pytest.mark.asyncio
-async def test_set_window_label_sets_option_and_format(runner):
-    """set_window_label sets @hqt_label + a label-aware window-status-format,
-    targeting the window by NAME (identity preserved — no rename)."""
-    from hqt.tmux.runner import WINDOW_STATUS_FORMAT
+async def test_set_window_label_sets_only_label_option(runner):
+    """set_window_label updates ONLY the dynamic @hqt_label, targeting the
+    window by NAME (identity preserved — no rename).
 
+    It must NOT (re)write window-status-format / window-status-current-format:
+    the format is static and is established once by new_window (creation) and
+    apply_theme (existing windows). Re-asserting it on every 3s poll is the
+    vehicle that lets a stale/competing writer flip the cell between padded and
+    unpadded — see the toggle bug this guards against.
+    """
     await runner.set_window_label("hqt-1", "◐ myproj")
     args = runner._exec.call_args.args
     # Targets by name (exact-match prefix), never renames the window.
     assert "hqt-main:=hqt-1" in args
     assert "@hqt_label" in args
     assert "◐ myproj" in args
-    # Both formats reference the label option so the bar shows it.
-    assert args.count(WINDOW_STATUS_FORMAT) == 2
-    assert "window-status-format" in args
-    assert "window-status-current-format" in args
+    # The poll does not touch the format — that is owned by new_window/apply_theme.
+    assert "window-status-format" not in args
+    assert "window-status-current-format" not in args
     # All in a single atomic tmux invocation.
     assert runner._exec.call_count == 1