feat(ui): right-rail companion chat — streaming, tool chips, inline drafts

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

public/state.js

@@ -1,5 +1,12 @@
 // Tiny event bus for cross-component state (pending count, agent toggle, etc.).
 // No reactive framework — just publish/subscribe with last-value semantics.
+//
+// `state` is a plain mutable object for values that don't need subscriptions.
+// Set by the app router on each navigation; read by components like the rail.
+export const state = {
+  spaceId: null,   // string | null — ID of the currently active Space
+  view: null,      // { entityType, entityId } | null — entity focused in main panel
+};
 
 const subs = new Map();   // event → Set<fn>
 const last = new Map();   // event → last value