feat(session-export): add command and Header action

apps/web/tests/snapshots/lifecycle-chrome/command-menu.expected.md

@@ -1,6 +1,7 @@
 - listbox "Trigger suggestions":
   - text: Commands
   - option "compact Compact older conversation history" [selected]
+  - option "export Download this Session log as a ZIP archive"
   - option "feedback record feedback about this session"
   - option "goal set or view the goal for a long-running task"
   - option "permission Switch the permission preset (sandbox mode + approval policy)"

apps/web/tests/snapshots/lifecycle-chrome/reloaded.expected.md

@@ -3,6 +3,9 @@
     - button "Reply with the single word" [disabled]
   - img
   - text: Standard mode
+  - button "Session log":
+    - text: Session log
+    - img
   - tablist:
     - tab "Chat" [selected]
     - tab "Trajectory"