fix(tui): move KV-persisted toggles from Session to System category

Move four command palette items that persist via KV store to the System
category for consistency:
- Show/Hide timestamps
- Show/Hide thinking
- Show/Hide tool details
- Show/Hide header

These toggles persist across sessions, so they belong in System rather
than Session.

Resolves #158

Author: ariane-emory

packages/opencode/src/cli/cmd/tui/routes/session/index.tsx

@@ -539,7 +539,7 @@ export function Session() {
     {
       title: showTimestamps() ? "Hide timestamps" : "Show timestamps",
       value: "session.toggle.timestamps",
-      category: "Session",
+      category: "System",
       slash: {
         name: "timestamps",
         aliases: ["toggle-timestamps"],
@@ -553,7 +553,7 @@ export function Session() {
       title: showThinking() ? "Hide thinking" : "Show thinking",
       value: "session.toggle.thinking",
       keybind: "display_thinking",
-      category: "Session",
+      category: "System",
       slash: {
         name: "thinking",
         aliases: ["toggle-thinking"],
@@ -567,7 +567,7 @@ export function Session() {
       title: showDetails() ? "Hide tool details" : "Show tool details",
       value: "session.toggle.actions",
       keybind: "tool_details",
-      category: "Session",
+      category: "System",
       onSelect: (dialog) => {
         setShowDetails((prev) => !prev)
         dialog.clear()
@@ -586,7 +586,7 @@ export function Session() {
     {
       title: showHeader() ? "Hide header" : "Show header",
       value: "session.toggle.header",
-      category: "Session",
+      category: "System",
       onSelect: (dialog) => {
         setShowHeader((prev) => !prev)
         dialog.clear()