feat(assistant): trip assistant chat with your own AI connection

Adds an in-app assistant that reads and plans the open trip. Users connect
their own provider (Sign in with ChatGPT, or an Anthropic, OpenAI, Gemini or
OpenRouter key) or use the one the admin set up, including a custom
OpenAI-compatible server. It is an addon and only shows while a connection
is usable.

The chat runs on the existing MCP tools, pinned to the trip. Every change is
held as a change card the user applies or discards, and applied changes can
be undone. On the desktop it is a floating window that can be moved and
resized; on the phone it is fullscreen. Search results show as place cards
that can go onto a day, weather lookups as a strip, proposed places as
ghost markers on the map with a before/after switch, and an answer can be
shared into the trip chat. Booking files can be dropped in and are read
into change cards.

client/src/components/Map/mapViewContract.ts

@@ -197,6 +197,58 @@ export interface MapViewProps {
    * it; the Leaflet renderer takes the prop and never calls it.
    */
   onMapReady?: (map: CompassMap | null) => void;
+  /** The assistant's suggestions that are not on the map yet, drawn as dashed pins outside the clusters. */
+  assistantGhosts?: AssistantGhost[];
+  /** The suggestion under the pointer, in the chat or on the map; its ghost pulses. */
+  assistantHoveredId?: string | null;
+  onAssistantGhostHover?: (id: string | null) => void;
+  onAssistantGhostClick?: (id: string) => void;
+  /** A place already on the map that the hovered suggestion is about; its own pin pulses instead of a ghost. */
+  assistantPulsePlaceId?: number | null;
+  /** Where the assistant asks the map to look; a new `key` is a new request. */
+  assistantCamera?: AssistantCamera | null;
+  /** Places that just arrived from an applied suggestion; their pins pop once. */
+  poppedPlaceIds?: readonly number[];
+  /** While the map shows the plan before a change, its pins cannot be dragged onto a day. */
+  markersLocked?: boolean;
+}
+
+/** The assistant's part of the contract, which both renderers hand to their assistant modules whole. */
+export type AssistantMapProps = Pick<
+  MapViewProps,
+  | 'assistantGhosts'
+  | 'assistantHoveredId'
+  | 'onAssistantGhostHover'
+  | 'onAssistantGhostClick'
+  | 'assistantPulsePlaceId'
+  | 'assistantCamera'
+  | 'poppedPlaceIds'
+  | 'markersLocked'
+>;
+
+/** A suggested place drawn before it exists. `color` and `icon` are its category's. */
+export interface AssistantGhost {
+  id: string;
+  lat: number;
+  lng: number;
+  name: string;
+  color?: string;
+  icon?: string;
+}
+
+/**
+ * A camera move the assistant asks for. `fit` frames all points, `pan` only
+ * brings their centre into view when it is outside. `auto` marks a move the
+ * user did not ask for: the map skips it while the user is moving the map
+ * themselves. `cover` is what the assistant's window hides of the map.
+ */
+export interface AssistantCamera {
+  key: string;
+  points: [number, number][];
+  mode: 'fit' | 'pan';
+  animate: boolean;
+  auto: boolean;
+  cover?: { side: 'left' | 'right'; px: number } | null;
 }
 
 /**