feat: Simplify AI Engine settings screen

[thejaustin]

Summary

LLMSettingsPreferences.kt is extremely dense — it shows performance analytics, live logs, circuit breaker thresholds, force parallel streams, and API key config all on one screen. Non-technical users are overwhelmed by options like "Force Parallel Streams (HIGH RISK)".

Proposed Changes

• Move the following into a collapsible Advanced section:
  • Force Parallel Streams
  • Error Tolerance slider
  • Smart Fallback toggle
• Move live Engine Status / log viewer to the Diagnostics screen
• Keep top-level visible: provider selection, API key, model, Test Connection, accuracy cards

Acceptance Criteria

• Advanced section collapsed by default, remembers open state
• Live log viewer removed from AI Engine screen, accessible via Diagnostics
• Screen fits on one scroll without overwhelming non-technical users
• All existing functionality preserved