style: fix lint across client packages

eslint --fix autofixes plus manual repairs: max-len line splits
(fake-api handlers, notifier/slots JSDoc, spec signatures), charAt over
non-null-asserted indexing in slash detect/menu cores, Array.from for
code-point capping, typeof assertions for unbound-method in specs,
generic getByRole for the send-button cast, effect disposer void-wrap in
command register, and dropped unused type imports.

packages/client/ui-slash/tests/service.spec.ts

@@ -486,7 +486,7 @@ describe('pick / scoped input events', () => {
 })
 
 describe('lexicon', () => {
-  function lexSource(trigger: TriggerChar, name: string, roll?: readonly string[] | undefined, hasHook = true): SlashSource {
+  function lexSource(trigger: TriggerChar, name: string, roll?: readonly string[]  , hasHook = true): SlashSource {
     return {
       trigger,
       name,