[codex] persist panel time window preferences

[upsetbit]

Summary

• persist panel time-window filters per page through PreferencesService
• add a Settings default-window picker and reset action for theme/window preferences
• document the preference keys, routes, and Settings behavior

Validation

• go test ./internal/server/handlers -run Preferences
• go test ./internal/panel -run 'WindowPreference|Settings|HomeRenders|ProfilesRenders|LoadViews|SessionsRows'
• go test ./internal/panel/...
• just lint-md
• just gen-check
• just test

Pre-push hooks also ran markdown lint, link checks, agnix, gitleaks, and scripts/publish-npm.test.sh.

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