Use `key` prop to reset LLM role manager form state instead of useEffect sync

[MODSetter]

Description

In llm-role-manager.tsx, when server data changes (via preferences), a useEffect copies the new values into local state. This adds an extra re-render per data change. The recommended approach is to use a key prop so React remounts the form with correct initial state, and derive hasChanges during render.

Vercel React Best Practices Rule: rerender-derived-state-no-effect (5.1)

File to change

• surfsense_web/components/settings/llm-role-manager.tsx
• The parent component that renders LlmRoleManager

What to do

1. In the parent that renders LlmRoleManager, pass key={searchSpaceId} so the component remounts when the search space changes:

<LlmRoleManager key={searchSpaceId} searchSpaceId={searchSpaceId} />

2. Remove the sync useEffect (lines 124-132):

// DELETE:
useEffect(() => {
  const newAssignments = {
    agent_llm_id: preferences.agent_llm_id ?? "",
    document_summary_llm_id: preferences.document_summary_llm_id ?? "",
    image_generation_config_id: preferences.image_generation_config_id ?? "",
  };
  setAssignments(newAssignments);
  setHasChanges(false);
}, [preferences]);

3. Convert hasChanges to a derived value (remove the state variable):

// Remove: const [hasChanges, setHasChanges] = useState(false);
// Add:
const hasChanges =
  assignments.agent_llm_id !== (preferences.agent_llm_id ?? "") ||
  assignments.document_summary_llm_id !== (preferences.document_summary_llm_id ?? "") ||
  assignments.image_generation_config_id !== (preferences.image_generation_config_id ?? "");

4. Remove setHasChanges(false) from the save handler and any other places it appears.

Acceptance criteria

• No sync useEffect mirrors preferences into local state
• hasChanges is derived during render, not stored in state
• LLM role assignments still display correctly and save properly
• Switching search spaces resets the form to the new space's preferences

[camwillm]

I'd like to take this on. I'll remove the sync useEffect, convert hasChanges to a derived value, and add the key prop in the parent. PR incoming.