review: address Opus code-review findings on this branch

- config_flow: the #192 port-rescue made the "every port refused" fast-fail
  permanently unreachable (PREFERRED_PROBE_PORTS is always non-empty and
  always rescued), so removed the dead branch instead of leaving it as
  misleading dead code. A dead host now fails via the handshake loop's own
  error, which carries the real per-port reason.
- oven._has_option: added the is_stub_rep carve-out cooktop.py's identical
  per-token exists_fn already has on the same kind of href, so a not-yet
  sub-polled /mode/vs/0 doesn't permanently exclude energy_saving/
  cooktop_on_alert before their first real fetch lands.
- airconditioner.ENERGY_METER_LEGACY: build via dataclasses.replace() like
  its ENERGY_METER_GENERIC sibling, instead of hand-copying href/poll_tier
  (which would silently drift if common.ENERGY_METER ever gains a field).
- Fixed two stale comments: is_legacy_board()'s docstring still listed
  Volume among tokens needing legacy-only gating, though 'beep' now applies
  unconditionally across board generations; and common.py's UNIVERSAL
  invariant comment didn't mention that airconditioner also now excludes
  ENERGY_METER from the wholesale bundle.
- #191 (CAC token): added the fixture/golden/capability-test coverage the
  AVT token in the same branch got, including an honestly-documented list
  of the ten hrefs this board generation doesn't cover yet.
- fridge.cooler_temperature_setpoint: dropped the hardcoded "N °C" state
  labels -- the resource's own unit field isn't necessarily Celsius on a
  different model reporting the same href, and the options themselves are
  already read live via options_field, so a static per-value label risked
  asserting the wrong unit for a future device sharing this capability.
- airconditioner._legacy_cumulative_power_kwh: parse with float (matching
  common.wh_to_kwh's own numeric parsing) instead of this module's
  integer-only _int, so a decimal-formatted reading doesn't raise.
- test_config_flow: the port-rescue test bound the real 49154 directly,
  which could collide with an actually-running service on some machine;
  now monkeypatches PREFERRED_PROBE_PORTS to an OS-assigned port instead.
- oven.py: consolidated six byte-for-byte-identical single-token options
  write_fns (lamp/sound/fast_preheat/natural_steam/energy_saving/
  cooktop_on_alert) into one _option_switch_write(prefix) factory.

845 tests passing (up from 841 -- 4 new CAC coverage tests).

tests/test_golden_regression.py

@@ -859,6 +859,26 @@ def test_registry_reproduces_golden_state_keys_for_airconditioner_fac_bora():
     )
 
 
+def test_registry_reproduces_golden_state_keys_for_airconditioner_cac():
+    """TP1X_DA-AC-CAC-01001_0000 (issue #191) -- fell back to 'unknown' in
+    0.16.0 when oneUiVersion detection was dropped, since 'CAC' had never
+    been added to the modelNum board-token table. Resolved via the new 'CAC'
+    token onto the existing airconditioner registry. Not fully covered yet --
+    ten hrefs remain unbound (edge lighting, PM1 filter, stateful light,
+    absence-clean, four sound-settings resources, smart-sensing-cooling, UV
+    LED), all genuinely new to this board generation and out of scope for
+    the routing fix; see test_airconditioner_cac.py for the documented gap."""
+    from tests.conftest import _load_device
+    resources = _load_device('airconditioner_cac')
+    golden = json.loads((GOLDEN / 'airconditioner_cac.json').read_text())
+    state_keys = _new_state_keys('airconditioner_cac', resources)
+    assert set(state_keys) == set(golden['state_keys']), (
+        f"state_keys mismatch:\n"
+        f"  extra:   {sorted(set(state_keys) - set(golden['state_keys']))}\n"
+        f"  missing: {sorted(set(golden['state_keys']) - set(state_keys))}"
+    )
+
+
 def test_registry_reproduces_golden_state_keys_for_air_purifier_avt_ww():
     """AVT-WW-TP1-23-AXX500 (issue #190) -- next-gen BESPOKE Cube Air board;
     reports device_type 'unknown' with empty oneUiVersion because 'VTWW' as a