Clean up remaining dead code and dependencies

- Replace unused 'codemirror' barrel dep with explicit @codemirror/{state,
  view,commands,language} sub-packages that were imported but unlisted
- Remove unused exports: writeNamespacedQuery, targetWorkspacePathForRun,
  isWorkspaceDeletionRun, piWebConfigDir, duplicate parsePiWebRuntimeResponse
- Remove unused types: WorkspacePanelFiles, WorkspacePanelHost,
  GetActiveSession, SaveAttachmentsResponse, QueryValues
- Drop now-unused re-exports/imports cascading from the above
- Add knip config + 'npm run knip' script for ongoing dead-code detection

src/shared/apiTypes.ts

@@ -175,10 +175,6 @@ export interface SavedPromptAttachment {
   size: number;
 }
 
-export interface SaveAttachmentsResponse {
-  attachments: SavedPromptAttachment[];
-}
-
 export interface SessionModel {
   provider?: string;
   id?: string;