Port missing features to gui_2 and optimize caching

- Port 10 missing features from gui.py to gui_2.py: performance
    diagnostics, prior session log viewing, token budget visualization,
    agent tools config, API hooks server, GUI task queue, discussion
    truncation, THINKING/LIVE indicators, event subscriptions, and
    session usage tracking
  - Persist window visibility state in config.toml
  - Fix Gemini cache invalidation by separating discussion history
    from cached context (use MD5 hash instead of built-in hash)
  - Add cost optimizations: tool output truncation at source, proactive
    history trimming at 40%, summary_only support in aggregate.run()
  - Add cleanup() for destroying API caches on exit

config.toml

@@ -18,3 +18,17 @@ paths = [
     "C:/projects/forth/bootslop/bootslop.toml",
 ]
 active = "manual_slop.toml"
+
+[gui.show_windows]
+Projects = true
+Files = true
+Screenshots = true
+"Discussion History" = true
+Provider = true
+Message = true
+Response = true
+"Tool Calls" = true
+"Comms History" = true
+"System Prompts" = true
+Theme = true
+Diagnostics = true