docs(agent-inspector): sync thinking_level comments with no-override semantics (MUL-2339)

Follow-up to #2919 review nits — comments still described the empty
thinking_level as "use runtime default" and claimed ThinkingPicker callers
guaranteed non-empty levels. Both were stale after the semantics changed:

- packages/core/types/agent.ts: clarify that "" clears the override and
  the local CLI config / built-in default decides at runtime.
- thinking-picker.tsx: document that the stale-orphan clear path in
  ThinkingPropRow mounts the picker with an empty levels list plus a
  persisted value, so callers do not guarantee non-empty levels.

Co-authored-by: multica-agent <github@multica.ai>

packages/core/types/agent.ts

@@ -267,7 +267,8 @@ export interface UpdateAgentRequest {
   /**
    * Runtime-native reasoning/effort token. Tri-state semantics (MUL-2339):
    *   - field omitted → no change
-   *   - "" → explicit clear (use runtime default)
+   *   - "" → clear the override; backend omits the effort flag and the
+   *     local CLI config / built-in default decides what the model runs at
    *   - non-empty → set; validated server-side against the target
    *     runtime's provider enum, rejected with 400 if not recognised
    */

packages/views/agents/components/inspector/thinking-picker.tsx

@@ -31,8 +31,10 @@ export function ThinkingPicker({
 }: {
   /** Persisted thinking_level — "" means "follow local CLI config". */
   value: string;
-  /** Supported levels for the current (runtime, model) pair. Caller has
-   *  already verified the list is non-empty before mounting this picker. */
+  /** Supported levels for the current (runtime, model) pair. Usually
+   *  non-empty when the row is shown, but the stale-orphan clear path
+   *  in ThinkingPropRow mounts the picker with an empty list plus a
+   *  persisted value so the user can see and clear the dangling token. */
   levels: RuntimeModelThinkingLevel[];
   /** When false, render a static read-only display and skip the popover. */
   canEdit?: boolean;