Add panel-plane API client with config plumbing (Feature 18)

The integration will consume the NestQuest API service (Feature 16) over
HTTP instead of reading the database. This adds the one module that
speaks the panel plane: api_client.py with get_snapshot() and
complete_instance(), a typed NestQuestApiError for transport failures
and non-2xx responses (carrying the HTTP status so 401/404 are
distinguishable), one timeout per request and no retry loops. The HTTP
session is injected, so tests exercise the client against a stub
transport with no network and no aiohttp; the production factory hands
in HA's shared aiohttp session and resolves the base URL and panel
service token off the config entry (options, then entry data, then
defaults). The two new settings are wired into the options flow like
every other section (validation mirrored with the client's constructor
rules); the token is a secret and is never logged or echoed into error
messages. Coordinator wiring is the next task.

custom_components/nestquest/options_flow.py

@@ -12,6 +12,7 @@ from .const import (
     CONF_ADMIN_USER_IDS,
     CONF_AFTERNOON_REMINDER_ENABLED,
     CONF_AFTERNOON_REMINDER_TIME,
+    CONF_API_BASE_URL,
     CONF_CELEBRATION_ENABLED,
     CONF_DAY_ROLLOVER_TIME,
     CONF_END_OF_DAY_REPORT_ENABLED,
@@ -21,7 +22,9 @@ from .const import (
     CONF_MORNING_SUMMARY_TIME,
     CONF_NOTIFY_TARGET,
     CONF_PANEL_IDLE_TIMEOUT,
+    CONF_PANEL_TOKEN,
     CONF_UPDATE_INTERVAL,
+    DEFAULT_API_BASE_URL,
     DEFAULT_AFTERNOON_REMINDER_TIME,
     DEFAULT_AUTOMATION_ENABLED,
     DEFAULT_DAY_ROLLOVER_TIME,
@@ -29,12 +32,14 @@ from .const import (
     DEFAULT_HORIZON_DAYS,
     DEFAULT_MORNING_SUMMARY_TIME,
     DEFAULT_PANEL_IDLE_TIMEOUT,
+    DEFAULT_PANEL_TOKEN,
     DEFAULT_UPDATE_INTERVAL,
     DOMAIN,
     MIN_UPDATE_INTERVAL,
     TIME_PATTERN,
 )
 from .admin_allowlist import list_admin_ids, set_admin_ids
+from .api_client import is_valid_base_url
 
 MIN_HORIZON_DAYS = 1
 MIN_PANEL_IDLE_TIMEOUT = 30
@@ -116,6 +121,25 @@ def _async_validate(user_input: dict[str, Any]) -> dict[str, str]:
         if toggle_value is not None and not isinstance(toggle_value, bool):
             errors[toggle_key] = "invalid"
 
+    # The panel-plane API connection (Feature 18) is OPTIONAL in raw
+    # submits the same way: a missing key keeps the current value.  The
+    # base URL must be a full http(s) URL with a host — the same check
+    # the client's constructor enforces, so a malformed URL fails at
+    # the form, not at the first request.  The token may be EMPTY (the
+    # API connection is simply not configured yet) but a non-empty one
+    # must be pasted unpadded: a padded or whitespace-only value is a
+    # clipboard mistake that would fail the token check at request
+    # time.
+    api_base_url = user_input.get(CONF_API_BASE_URL)
+    if api_base_url is not None and not is_valid_base_url(api_base_url):
+        errors[CONF_API_BASE_URL] = "invalid_url"
+    panel_token = user_input.get(CONF_PANEL_TOKEN)
+    if panel_token is not None and (
+        not isinstance(panel_token, str)
+        or panel_token != panel_token.strip()
+    ):
+        errors[CONF_PANEL_TOKEN] = "invalid"
+
     return errors
 
 
@@ -186,6 +210,18 @@ def _build_schema(
             CONF_CELEBRATION_ENABLED,
             default=current[CONF_CELEBRATION_ENABLED],
         ): _strict_bool,
+        # Panel-plane API connection (Feature 18): the base URL the API
+        # client talks to and the panel service token it presents as
+        # the Bearer credential.  Schema-validated submits always carry
+        # both (the defaults pre-fill from the stored values); raw
+        # callers omitting them keep their stored values (see
+        # _async_validate).
+        vol.Required(
+            CONF_API_BASE_URL, default=current[CONF_API_BASE_URL]
+        ): str,
+        vol.Required(
+            CONF_PANEL_TOKEN, default=current[CONF_PANEL_TOKEN]
+        ): str,
     }
     if admin_choices is not None:
         # HA's supported multi-select validator: the frontend can
@@ -336,6 +372,11 @@ class NestQuestOptionsFlow(config_entries.OptionsFlowWithConfigEntry):
             data[notification_key] = user_input.get(
                 notification_key, current[notification_key]
             )
+        # The API connection section (Feature 18) stores the base URL
+        # and panel token the same fall-back-to-current way, so raw
+        # submits that predate the section keep their stored values.
+        for api_key in (CONF_API_BASE_URL, CONF_PANEL_TOKEN):
+            data[api_key] = user_input.get(api_key, current[api_key])
         if admin_ids_present:
             data[CONF_ADMIN_USER_IDS] = admin_ids
         elif admin_default:
@@ -365,6 +406,8 @@ class NestQuestOptionsFlow(config_entries.OptionsFlowWithConfigEntry):
             (CONF_AFTERNOON_REMINDER_ENABLED, DEFAULT_AUTOMATION_ENABLED),
             (CONF_END_OF_DAY_REPORT_ENABLED, DEFAULT_AUTOMATION_ENABLED),
             (CONF_CELEBRATION_ENABLED, DEFAULT_AUTOMATION_ENABLED),
+            (CONF_API_BASE_URL, DEFAULT_API_BASE_URL),
+            (CONF_PANEL_TOKEN, DEFAULT_PANEL_TOKEN),
         ):
             if key in options:
                 values[key] = options[key]