feat: print includes answer only after unlocking solutions

- If solutions already unlocked (full mode), print button shows '打印题目+答案'
- If not unlocked, print button shows '打印题目' (problem only)
- No longer forces unlock when printing

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

remote_patch_cpp_basic_20.py

@@ -0,0 +1,43 @@
+#!/usr/bin/env python3
+from __future__ import annotations
+
+import argparse
+from pathlib import Path
+
+
+def main():
+    ap = argparse.ArgumentParser()
+    ap.add_argument('--file', required=True)
+    ap.add_argument('--items', required=True)
+    args = ap.parse_args()
+
+    p = Path(args.file)
+    items = Path(args.items).read_text(encoding='utf-8')
+    s = p.read_text(encoding='utf-8')
+
+    marker = 'const CourseItem items[] = {'
+    i = s.find(marker)
+    if i < 0:
+        raise SystemExit(f'cannot find marker: {marker}')
+
+    j = s.find('};', i)
+    if j < 0:
+        raise SystemExit('cannot find end marker "};" after items start')
+
+    before = s[:i]
+    after = s[j+2:]
+
+    out = before + items + after
+    if out == s:
+        print('no change')
+        return
+
+    backup = p.with_suffix(p.suffix + '.bak_cppbasic20')
+    backup.write_text(s, encoding='utf-8')
+    p.write_text(out, encoding='utf-8')
+    print('patched', str(p))
+    print('backup', str(backup))
+
+
+if __name__ == '__main__':
+    main()