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_tui.py

@@ -1057,3 +1057,76 @@ async def test_rename_session_opens_prefilled_and_updates():
         assert app._db_session.get(Session, sess.id).nickname == "after"
 
 
+# ---------------------------------------------------------------------------
+# Vim-style j/k navigation in the project and session lists
+# ---------------------------------------------------------------------------
+
+
+@pytest.mark.asyncio
+async def test_project_list_jk_navigation():
+    """j/k move the highlight down/up in the project list like the arrow keys."""
+    app = HqtApp()
+    async with app.run_test(size=(120, 40)) as pilot:
+        from hqt.tui.widgets.project_list import ProjectList
+
+        p1 = app._project_service.create("first", "/tmp/jk-first")
+        p2 = app._project_service.create("second", "/tmp/jk-second")
+        app._load_projects()
+        await app.workers.wait_for_complete()
+        await pilot.pause()
+
+        pl = app.query_one(ProjectList)
+        pl.query_one("#project-list").focus()
+        await pilot.pause()
+        # j walks down to the second project...
+        await pilot.press("j")
+        await pilot.pause()
+        assert pl.get_selected_project_id() == p2.id
+        # ...and k walks back up to the first.
+        await pilot.press("k")
+        await pilot.pause()
+        assert pl.get_selected_project_id() == p1.id
+
+
+@pytest.mark.asyncio
+async def test_session_list_jk_navigation():
+    """j/k move the highlight down/up in the session list like the arrow keys."""
+    from hqt.db.models import Harness, Project, Session
+    from hqt.tui.widgets.session_list import SessionList
+
+    app = HqtApp()
+    async with app.run_test(size=(120, 40)) as pilot:
+        proj = Project(name="jk-proj", path="/tmp/jk-proj")
+        app._db_session.add(proj)
+        app._db_session.flush()
+        harness = app._db_session.query(Harness).first()
+        sessions = []
+        for n in range(2):
+            s = Session(
+                project_id=proj.id,
+                harness_id=harness.id,
+                nickname=f"sess-{n}",
+                tmux_session_name=f"hqt-jk-{n}",
+                archived=False,
+            )
+            app._db_session.add(s)
+            sessions.append(s)
+        app._db_session.commit()
+
+        app._selected_project_id = proj.id
+        # restore_selection mirrors a real project switch, which highlights the
+        # first session — giving j/k a defined starting point.
+        await app._refresh_sessions(restore_selection=True)
+        await pilot.pause()
+
+        sl = app.query_one(SessionList)
+        sl.query_one("#session-list").focus()
+        await pilot.pause()
+        await pilot.press("j")
+        await pilot.pause()
+        assert sl.get_selected_session_id() == sessions[1].id
+        await pilot.press("k")
+        await pilot.pause()
+        assert sl.get_selected_session_id() == sessions[0].id
+
+