chore(lint): clear the semantic .tsx backlog

Hand fixes for the findings --fix cannot touch, mirroring the fixes
already applied on the fe-docs feature branch (same file, same shape)
so its eventual rebase resolves cleanly:

- restore the return the no-confusing-void-expression autofix ate in
  useAbsentSnapshot (typed S | undefined; hook call kept for hook-order
  stability, undefined returned explicitly);
- re-type DOM queries the no-unnecessary-type-assertion autofix broke:
  getByRole<HTMLButtonElement>(...) generics instead of the removed
  as-casts (the eslint program and the client tsconfig aggregate
  disagree about these casts; the generic form satisfies both);
- justified eslint-disable for the deliberate legacy paths: keyCode 229
  IME-composition detection, execCommand clipboard fallbacks, lib.dom
  clipboard optionality, and the any-typed Reflect.get/this probes in
  test fakes;
- drop the dead react/no-danger directive (eslint-plugin-react is not
  loaded, so the rule never applied) keeping its shiki rationale;
- delete the tautological 'Z' comparison and the renameTarget null
  check already implied by renameBlocked;
- css-module non-null assertions replaced by type widening
  (Button className, TAG_CLASS Record) per the established pattern;
- misc: max-len comment wraps, void generic drop in the deferred test
  helper, unused type imports, floating selectWorkspace promises voided,
  member-delimiter newlines in inline type literals.

packages/client/ui-primitives/src/Button.tsx

@@ -19,7 +19,7 @@ export function Button({ variant = 'ghost', size = 'md', icon, className, childr
   variant?: ButtonVariant
   size?: 'md' | 'sm'
   icon?: ReactNode
-  className?: string
+  className?: string | undefined
   children?: ReactNode
 } & ButtonHTMLAttributes<HTMLButtonElement>) {
   return (