Auto-register the zero-config panel dashboard on setup

A fresh HA install with children configured should show the panel
with no YAML and no manual dashboard creation: setup now registers
ONE storage-mode Lovelace dashboard whose config is the bundle's
custom:nestquest-party strategy (frontend/src/strategy.ts), under the
stable url_path 'nestquest' with a title, icon and sidebar visibility.
Registration is idempotent — the url_path is the idempotency key, so
a reload or a second entry never duplicates the dashboard, and a
dashboard already occupying the url_path (ours or the user's) is left
completely alone (never overwritten, never deleted).  An unavailable
Lovelace dashboards collection (YAML mode, lovelace not loaded) or a
refused create logs a clear warning and setup continues — never a
crash.  Tests cover create-on-setup, no-duplicate-on-reload, the
untouched user dashboard, the missing collection and a refusing one.

custom_components/nestquest/core/const.py

@@ -43,6 +43,18 @@ DOMAIN_SERVICES: tuple[str, ...] = (
 
 SQLITE_DB_FILENAME = "nestquest.db"
 
+# Zero-config panel dashboard (Feature 20): ONE storage-mode Lovelace
+# dashboard registered on setup whose config carries the bundle's
+# ``custom:nestquest-party`` strategy (frontend/src/strategy.ts) — the
+# views are generated at render time from the household roster.  The
+# url_path IS the domain: the stable key idempotency is keyed on (a
+# reload or a second entry never duplicates it, and a dashboard already
+# registered under it — ours or the user's — is left untouched).
+DASHBOARD_URL_PATH = DOMAIN
+DASHBOARD_TITLE = "NestQuest"
+DASHBOARD_ICON = "mdi:party-popper"
+DASHBOARD_STRATEGY_TYPE = "custom:nestquest-party"
+
 # Configuration keys and default values
 CONF_HORIZON_DAYS = "horizon_days"
 DEFAULT_HORIZON_DAYS = 14