fix(vscode): keep relative path in selection attachment filename (#1923)

The "Add to Context" command and the active-editor pin-selection suggestion both create selection attachments but used the basename only (e.g. assist.ts:47). OpenCode synthesizes its Read call from that filename, so the directory was lost and the model could read or edit the wrong file when names collide.

Use the workspace-relative path (asRelativePath(uri, false)) in both paths so the filename carries the directory and the two paths produce identical filenames, restoring attachment dedup.

Fixes #1914

packages/ui/src/components/chat/FileAttachment.tsx

@@ -471,7 +471,7 @@ export const ActiveEditorFileSuggestion = memo(() => {
       ? `${selection.startLine}`
       : `${selection.startLine}-${selection.endLine}`
   }
-  const selectionLabel = selection ? `${fileName}:${selectionRange}` : ''
+  const selectionLabel = selection ? `${relativePath}:${selectionRange}` : ''
   const isSelectionAttached = !!selectionLabel && attachedFiles.some(
     (f) => f.source === 'vscode' && f.vscodeSource === 'selection' && f.filename === selectionLabel && f.vscodePath === filePath
   )