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-slots/tests/type-chain.spec.tsx

@@ -41,7 +41,7 @@ function createPanelStore() {
   })
 }
 
-const chatStore = () => defineStore({
+const _chatStore = () => defineStore({
   init: () => ({ selection: null as { id: string } | null, draft: '' }),
   actions: {
     select: (d, t: { id: string }) => { d.selection = t },
@@ -49,7 +49,7 @@ const chatStore = () => defineStore({
     clearDraft: (d) => { d.draft = '' },
   },
 })
-type ChatHandle = ReturnType<typeof chatStore>
+type ChatHandle = ReturnType<typeof _chatStore>
 
 type FrameProps =
   & PropsRuntime<'chain.frame'>
@@ -211,7 +211,7 @@ describe('terminal-design type chain', () => {
       // @ts-expect-error non-chain keys have no renderSlotChain dispatch
       chainSlots.renderSlotChain('chain.conv', {})
       // @ts-expect-error a children set without chain keys provides no renderSlotChain
-      fp.renderSlotChain
+      type _NoChainSeat = typeof fp.renderSlotChain
 
       // renderSlot owner share typed at the call site.
       // @ts-expect-error owner shape mismatch (width missing)