fix(editor): keep file basename in @-reference links

The explorer @ button appended plain text (@folder/file.ts), which DSH's
composer only decorates as a folder ref (@folder/) — the file name stayed
outside the link. Insert FILE references through DSH's own structured
insert-reference event instead, minting one chip for the whole reference
(displayed as @basename, serialized as the full @path). Directories keep the
plain @dir/ mention so folder completion still works.

src/context-types.ts

@@ -391,9 +391,10 @@ export interface SidebarLocaleService {
 
 /** The composer draft face the sidebar reaches through `ctx.conversation.input`. */
 export interface SidebarSessionInput {
-  /** The live input store (draft read for append). */
+  /** The live input store (draft read for append). `draftRev` is the machine's
+   *  span-CAS revision — required to mint a structured file-reference chip. */
   state: {
-    getSnapshot(): { draft: string }
+    getSnapshot(): { draft: string; draftRev?: number }
   }
   /** Replace the draft text (the input machine's single public write path). */
   setDraft(text: string): void