refactor: decompose AgentSettingsBehaviorPageView + remove kyleosophy (#24141)

- Remove Kyleosophy alternative completion chimes (keeps original chime
intact)
- Extract 5 sub-components from the 717-line god component:
  - `PersonalInstructionsSettings` — user prompt textarea form
- `SystemInstructionsSettings` — admin system prompt + TextPreviewDialog
  - `VirtualDesktopSettings` — admin desktop toggle
  - `WorkspaceAutostopSettings` — admin autostop toggle + duration form
  - `RetentionPeriodSettings` — admin retention toggle + number input
- Parent is now a ~160-line layout shell
- `isAnyPromptSaving` coupling preserved via prop
- Add `docs/plans/` to `.gitignore`

> 🤖 Written by a Coder Agent. Reviewed by a human.

.gitignore

@@ -103,3 +103,6 @@ PLAN.md
 
 # Ignore any dev licenses
 license.txt
+-e 
+# Agent planning documents (local working files).
+docs/plans/