feat(ui,db,cmd): reduce dublicate code in window subwin logic, unify SQLite helpers, NULL checks added

window.c: add _get_subwin_cols, _apply_split_resize, _check_subwin_width; refactor show/hide/resize/refresh/update
database.c: add _db_prepare_ctx, _db_teardown; safer init/queries with fallback timestamp
cmd_defs.c: guard fopen in docgen; inputwin.c: replace assert with runtime check

src/ui/inputwin.c

@@ -144,10 +144,13 @@ void
 create_input_window(void)
 {
     /* MB_CUR_MAX is evaluated at runtime depending on the current
-     * locale, therefore we check that our own version is big enough
-     * and bail out if it isn't.
+     * locale; ensure our own compiled-in maximum is sufficient.
+     * Fail gracefully instead of aborting in production.
      */
-    assert(MB_CUR_MAX <= PROF_MB_CUR_MAX);
+    if (MB_CUR_MAX > PROF_MB_CUR_MAX) {
+        cons_show_error("Your locale's MB_CUR_MAX (%zu) exceeds PROF_MB_CUR_MAX (%d); input window disabled.", (size_t)MB_CUR_MAX, PROF_MB_CUR_MAX);
+        return;
+    }
 #ifdef NCURSES_REENTRANT
     set_escdelay(25);
 #else