feat(assistant): the assistant opens outside a trip, as a home chat about all trips

A third scope, home, next to trip and journey: threads that name neither a
trip nor a journey (the CHECK now only forbids both), reached under
/api/assistant by their owner only. A home turn reads the user's trips
through list_trips into a short card (under way, next, later, behind,
undated), offers every read (a trip's on the id the model names, checked by
the tool with the user's rights) and only the writes that take no trip or
journey (atlas, vacation planner, collections, tour library, settings), all
held as change cards. open_trip_chat answers with a card that goes on in
that trip's own chat with the question waiting in its composer.

On the desktop the window opens on the home chat outside a trip; its head
lists the trips to switch into and a switched trip chat has the way back.
On the phone the home chat opens full screen from the dashboard head and the
dock's More list, and the card opens the trip with its chat. Both run on
useAssistantHome.

client/scripts/feature-pairs.json

@@ -69,6 +69,15 @@
       "desktop": ["src/components/Assistant/AssistantWindow.tsx"],
       "mobile": ["src/mobile/screens/trip/assistant/MAssistantScreen.tsx"]
     },
+    {
+      "feature": "AI assistant home chat",
+      "hooks": ["src/components/Assistant/useAssistantHome.ts"],
+      "desktop": ["src/components/Assistant/AssistantWindow.tsx"],
+      "mobile": [
+        "src/mobile/screens/assistant/MAssistantHomeScreen.tsx",
+        "src/mobile/screens/dashboard/MDashboard.tsx"
+      ]
+    },
     {
       "feature": "Assistant hints",
       "hooks": ["src/components/Assistant/useAssistantHints.ts"],