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/runtime/tests/queue-store.spec.ts

@@ -50,7 +50,7 @@ describe('queue intake', () => {
     const session = makeSession()
     session.handleMuxEnvelope(rid('env-3'), queuedFrame('长'.repeat(201), 'p-cap'))
     const preview = session.getSnapshot().queue[0]?.preview ?? ''
-    expect([...preview]).toHaveLength(201) // 200 + …
+    expect(Array.from(preview)).toHaveLength(201) // 200 + …
     expect(preview.endsWith('…')).toBe(true)
   })