fix(frontend): repair staging breakpoint and focus contracts

Merge entry overflow rules into the existing 480px breakpoint, restore picker focus without scrolling, and sync composer and entry contracts without changing page logic. Add AST generation-state guard and both picker close-path regressions.

Validation: targeted 33/33; Chrome isolated components 145 checks; tsc and lint zero errors. Node22 full suite 3706 tests, no lost names or new failures; three target failures fixed, 88 baseline environment/contract failures unchanged. Windows build remains blocked by symlink EPERM. Changed-file privacy check: 11 files, no findings, not a full-repository pass. BUG-1011 remains separate.

Co-Authored-By: Claude Code <noreply@anthropic.com>

frontend/src/components/chat-profile-picker.tsx

@@ -46,7 +46,7 @@ export function ChatProfilePicker({
 
   function closePicker() {
     setOpen(false);
-    triggerRef.current?.focus();
+    triggerRef.current?.focus({ preventScroll: true });
   }
 
   async function choose(row: ChatProfilePickerRow) {
@@ -78,7 +78,7 @@ export function ChatProfilePicker({
       open={open}
       onOpenChange={(next) => {
         setOpen(next);
-        if (!next) triggerRef.current?.focus();
+        if (!next) triggerRef.current?.focus({ preventScroll: true });
       }}
     >
       <Popover.Trigger