Fix cookie-jar pollution; remove dead QR login code; add tests

The reauth flow ran validate_jsessionid against HA's shared aiohttp
session, then update_cookies({"JSESSIONID": ...}) added the new value
with no domain. aiohttp's cookie jar still held the previous
JSESSIONID pinned to smartthingsfind.samsung.com (set via Set-Cookie
during the previous load), and aiohttp prefers the more-specific
domain match — so the *stale* cookie went out, Samsung returned no
_csrf header, and the user saw "Cookie was rejected by SmartThings
Find" even though their cookie was fine.

Two fixes:

* validate_jsessionid now runs in an isolated aiohttp.ClientSession
  with its own jar, so the shared HA jar can't shadow the cookie
  under test.

* async_setup_entry clear_domain()s the smartthingsfind.samsung.com
  cookies before reseating JSESSIONID with response_url, otherwise
  the same shadowing breaks the entry reload that follows a
  successful UI reauth.

Also remove the QR-code login code (do_login_stage_one / _two,
gen_qr_code_base64, the legacy URL constants and qrcode/base64/
random/string/re/asyncio/io/timedelta imports) — Samsung migrated
account.samsung.com to a SPA-driven IAM/OAuth2 flow months ago, so
the QR scrape no longer works and nothing in the integration
references those helpers anymore. Drops the qrcode/pillow/requests
manifest requirements.

Tests: a minimal conftest stubs the homeassistant.* imports the
integration uses, and four async tests cover validate_jsessionid
including the regression case where a domain-bound stale cookie
sits in the shared jar.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

tests/conftest.py

@@ -0,0 +1,158 @@
+"""Stub the HA imports the integration touches so utils/config_flow can be
+imported and exercised without a full Home Assistant install.
+
+Only the bits used by the code under test are faked — anything new the
+integration starts touching will need to be added here."""
+from __future__ import annotations
+
+import sys
+import types
+from pathlib import Path
+from typing import Any
+
+REPO_ROOT = Path(__file__).resolve().parent.parent
+sys.path.insert(0, str(REPO_ROOT))
+
+
+def _module(name: str) -> types.ModuleType:
+    if name not in sys.modules:
+        sys.modules[name] = types.ModuleType(name)
+    return sys.modules[name]
+
+
+# homeassistant.core
+ha = _module("homeassistant")
+core = _module("homeassistant.core")
+
+
+class HomeAssistant:
+    def __init__(self) -> None:
+        self.data: dict[str, Any] = {}
+        # Tests assign a real aiohttp.ClientSession here.
+        self.clientsession = None
+
+
+def callback(func):
+    return func
+
+
+core.HomeAssistant = HomeAssistant
+core.callback = callback
+ha.core = core
+
+# homeassistant.exceptions
+exc = _module("homeassistant.exceptions")
+
+
+class ConfigEntryAuthFailed(Exception):
+    pass
+
+
+class ConfigEntryNotReady(Exception):
+    pass
+
+
+exc.ConfigEntryAuthFailed = ConfigEntryAuthFailed
+exc.ConfigEntryNotReady = ConfigEntryNotReady
+
+# homeassistant.helpers + submodules
+helpers = _module("homeassistant.helpers")
+aiohttp_client = _module("homeassistant.helpers.aiohttp_client")
+
+
+def async_get_clientsession(hass: HomeAssistant):
+    return hass.clientsession
+
+
+aiohttp_client.async_get_clientsession = async_get_clientsession
+helpers.aiohttp_client = aiohttp_client
+
+entity = _module("homeassistant.helpers.entity")
+
+
+class DeviceInfo(dict):
+    pass
+
+
+entity.DeviceInfo = DeviceInfo
+helpers.entity = entity
+
+device_registry = _module("homeassistant.helpers.device_registry")
+
+
+class _FakeDeviceRegistry:
+    def async_get_device(self, identifiers):
+        return None
+
+
+def _async_get(_hass):
+    return _FakeDeviceRegistry()
+
+
+device_registry.async_get = _async_get
+helpers.device_registry = device_registry
+
+typing_module = _module("homeassistant.helpers.typing")
+typing_module.ConfigType = dict
+
+# config_entries
+config_entries = _module("homeassistant.config_entries")
+
+
+class ConfigEntry:
+    pass
+
+
+class ConfigFlow:
+    def __init_subclass__(cls, *, domain=None, **kwargs):
+        super().__init_subclass__(**kwargs)
+
+
+class OptionsFlow:
+    pass
+
+
+class OptionsFlowWithConfigEntry(OptionsFlow):
+    def __init__(self, config_entry):
+        self.config_entry = config_entry
+        self.options = dict(getattr(config_entry, "options", {}) or {})
+
+
+CONN_CLASS_CLOUD_POLL = "cloud_poll"
+ConfigFlowResult = dict
+
+config_entries.ConfigEntry = ConfigEntry
+config_entries.ConfigFlow = ConfigFlow
+config_entries.OptionsFlow = OptionsFlow
+config_entries.OptionsFlowWithConfigEntry = OptionsFlowWithConfigEntry
+config_entries.CONN_CLASS_CLOUD_POLL = CONN_CLASS_CLOUD_POLL
+config_entries.ConfigFlowResult = ConfigFlowResult
+
+# const
+const = _module("homeassistant.const")
+
+
+class Platform:
+    DEVICE_TRACKER = "device_tracker"
+    BUTTON = "button"
+    SENSOR = "sensor"
+
+
+const.Platform = Platform
+
+# update_coordinator
+update_coord = _module("homeassistant.helpers.update_coordinator")
+
+
+class DataUpdateCoordinator:
+    def __init__(self, *args, **kwargs):
+        pass
+
+
+class UpdateFailed(Exception):
+    pass
+
+
+update_coord.DataUpdateCoordinator = DataUpdateCoordinator
+update_coord.UpdateFailed = UpdateFailed
+helpers.update_coordinator = update_coord