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/config.ts

@@ -197,6 +197,3 @@ export function examplePiWebConfig(config: PiWebConfig = {}): string {
   return `${JSON.stringify({ host: config.host ?? "127.0.0.1", port: config.port ?? 8504, allowedHosts: config.allowedHosts ?? [] }, null, 2)}\n`;
 }
 
-export function piWebConfigDir(env: NodeJS.ProcessEnv = process.env): string {
-  return dirname(defaultPiWebConfigPath(env));
-}