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-layout/src/client/AppFrame.tsx

@@ -33,7 +33,10 @@ function DetailsColumn(props: { children?: ReactNode }) {
   return <div className={css.detailsCol}>{props.children}</div>
 }
 
-/** One drag handle: pointer capture, rAF-throttled dx reports against the drag-start origin. `side` keys the hover-reveal CSS to the owning column. */
+/**
+ * One drag handle: pointer capture, rAF-throttled dx reports against the drag-start origin.
+ * `side` keys the hover-reveal CSS to the owning column.
+ */
 function DragHandle(props: { side: 'sidebar' | 'details'; left: number; onStart: () => void; onDrag: (dx: number) => void; onEnd: () => void }) {
   const [dragging, setDragging] = useState(false)
   const origin = useRef(0)