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/src/client/sessions/notifier.ts

@@ -64,7 +64,10 @@ export class Notifier {
     for (const listener of this.listeners) listener()
   }
 
-  /** Pre-getSnapshot check: rebuild synchronously when dirty (read path before first subscribe / while unobserved). Notification stays pending. */
+  /**
+   * Pre-getSnapshot check: rebuild synchronously when dirty (read path
+   * before first subscribe / while unobserved). Notification stays pending.
+   */
   ensureFresh(): void {
     if (!this.dirty) return
     this.dirty = false

packages/client/runtime/src/client/sessions/session.ts

@@ -53,7 +53,7 @@ function queuePreviewOf(content: readonly ContentBlock[]): string {
   const flat = content
     .map(block => (block.type === 'text' ? block.text : `[${block.type}]`))
     .join(' ').replace(/\s+/g, ' ').trim()
-  const chars = [...flat]
+  const chars = Array.from(flat)
   return chars.length > QUEUE_PREVIEW_CHARS ? `${chars.slice(0, QUEUE_PREVIEW_CHARS).join('')}…` : flat
 }