feat(web): row-count selector on the Executions card

Adds a "Show" selector (10 / 25 / 50 / 100) to the card header and drops the
default row count from 15 to 10. The chosen value rides on the card's own
polling URL (`/executions?limit=N`), so it survives the 5s htmx refresh with no
client-side state; a config default outside those four is rendered as an extra
option instead of disappearing. The query is parsed permissively — a stale or
hand-edited polling URL clamps or falls back to the config default rather than
422-ing a card that would otherwise render.

Ordering is now explicit rather than inherited from whatever Gitea returns:
newest first, a not-yet-started (queued) run above everything, ties broken on
Gitea's run id so matrix runs sharing a timestamp keep a stable order.

tests/python/test_web_executions.py

@@ -352,6 +352,122 @@ def test_end_to_end_against_a_stubbed_gitea(
     assert "no run" not in resp.text
 
 
+# ── row-count selector ──────────────────────────────────────────────────────
+
+
+def _stub_limits(monkeypatch: pytest.MonkeyPatch) -> list[int | None]:
+    """Replace the operations call; return the log of limits it was given."""
+    limits: list[int | None] = []
+
+    def fake_list_executions(
+        _config: Config,
+        _vms: list[LiveVm],
+        *,
+        token: str | None,
+        limit: int | None = None,
+        **_kw: Any,
+    ) -> ExecutionsView:
+        limits.append(limit)
+        return ExecutionsView(runs=[], unmatched_vms=[], source="admin", error=None)
+
+    monkeypatch.setattr(app_module, "list_executions", fake_list_executions)
+    return limits
+
+
+def test_default_limit_is_ten(tmp_path: Path, monkeypatch: pytest.MonkeyPatch) -> None:
+    limits = _stub_limits(monkeypatch)
+    _install_fake_keyring(monkeypatch)
+    app = create_app(_make_config(tmp_path, token_cred=_PAT_CRED_NAME))
+    app.dependency_overrides[get_backend] = lambda: _FakeBackend([])
+    client = TestClient(app)
+
+    resp = client.get("/executions")
+
+    assert limits == [10]
+    assert '<option value="10" selected>10</option>' in resp.text
+    assert "newest first" in resp.text
+
+
+def test_selector_offers_the_choices_and_marks_the_current_one(
+    tmp_path: Path, monkeypatch: pytest.MonkeyPatch
+) -> None:
+    limits = _stub_limits(monkeypatch)
+    _install_fake_keyring(monkeypatch)
+    app = create_app(_make_config(tmp_path, token_cred=_PAT_CRED_NAME))
+    app.dependency_overrides[get_backend] = lambda: _FakeBackend([])
+    client = TestClient(app)
+
+    resp = client.get("/executions?limit=50")
+
+    assert limits == [50]
+    for choice in (10, 25, 50, 100):
+        assert f'value="{choice}"' in resp.text
+    assert '<option value="50" selected>50</option>' in resp.text
+    # The re-rendered card polls with the chosen limit, so it survives refreshes.
+    assert 'hx-get="/executions?limit=50"' in resp.text
+
+
+def test_config_default_outside_the_choices_still_appears(
+    tmp_path: Path, monkeypatch: pytest.MonkeyPatch
+) -> None:
+    _stub_limits(monkeypatch)
+    _install_fake_keyring(monkeypatch)
+    config = _make_config(tmp_path, token_cred=_PAT_CRED_NAME)
+    object.__setattr__(config.web, "executions_limit", 7)
+    app = create_app(config)
+    app.dependency_overrides[get_backend] = lambda: _FakeBackend([])
+    client = TestClient(app)
+
+    resp = client.get("/executions")
+
+    assert '<option value="7" selected>7</option>' in resp.text
+
+
+@pytest.mark.parametrize(
+    ("query", "expected"),
+    [
+        ("?limit=25", 25),
+        ("?limit=7", 7),  # not offered, but honoured
+        ("?limit=0", 1),  # clamped up
+        ("?limit=9999", 100),  # clamped down
+        ("?limit=-5", 1),
+        ("?limit=abc", 10),  # unparseable -> config default
+        ("?limit=", 10),
+        ("", 10),
+    ],
+)
+def test_limit_query_is_parsed_permissively(
+    tmp_path: Path, monkeypatch: pytest.MonkeyPatch, query: str, expected: int
+) -> None:
+    """A stale or hand-edited polling URL must never fail the card."""
+    limits = _stub_limits(monkeypatch)
+    _install_fake_keyring(monkeypatch)
+    app = create_app(_make_config(tmp_path, token_cred=_PAT_CRED_NAME))
+    app.dependency_overrides[get_backend] = lambda: _FakeBackend([])
+    client = TestClient(app)
+
+    resp = client.get(f"/executions{query}")
+
+    assert resp.status_code == 200
+    assert limits == [expected]
+
+
+def test_dashboard_renders_the_selector_at_the_config_default(
+    tmp_path: Path, monkeypatch: pytest.MonkeyPatch
+) -> None:
+    _stub_limits(monkeypatch)
+    _install_fake_keyring(monkeypatch)
+    _quiet_host(monkeypatch)
+    app = create_app(_make_config(tmp_path, token_cred=_PAT_CRED_NAME))
+    app.dependency_overrides[get_backend] = lambda: _FakeBackend([])
+    client = TestClient(app)
+
+    resp = client.get("/")
+
+    assert resp.status_code == 200
+    assert 'hx-get="/executions?limit=10"' in resp.text
+
+
 # ── 2. degraded states ──────────────────────────────────────────────────────