fix(ui): preserve messages in non-chat windows while scrolled

_win_printf dropped buffer append and render for any window in paged
state, but only WIN_CHAT can recover lost messages via chatwin_db_history()
on scroll-down. WIN_MUC, WIN_PRIVATE and WIN_AI have no such fallback, so
incoming and outgoing messages were silently lost when the user was viewing
history.

Introduce log_database_can_recover_messages() to check whether the DB
backend can replay messages (returns FALSE when PREF_DBLOG is "off",
"redact", or no backend is active). Gate the WIN_CHAT early return in
_win_printf() on this check: when recovery is impossible, fall through
and append to the buffer so messages remain visible on scroll-down.

Add a buffer-bottom reset in win_page_down() for non-chat windows.
WIN_SCROLL_REACHED_BOTTOM is only set on the is_chat DB branch, so
non-chat windows never clear paged on their own; reset paged and
unread_msg when the last line of the buffer reaches the screen.

Add missing scroll rendering for AI windows in the title bar draw
function, ensuring AI windows display their scrolled state consistently
with other window types.

Remove the manual paged/unread_msg reset before printing the user
message in cl_ev_send_ai_msg() -- it was a local workaround for the
same drop and is no longer needed.

src/database.c

@@ -61,6 +61,22 @@ integrity_issue_free(integrity_issue_t* issue)
     }
 }
 
+gboolean
+log_database_can_recover_messages(void)
+{
+    if (!active_db_backend) {
+        return FALSE;
+    }
+    auto_gchar gchar* pref_dblog = prefs_get_string(PREF_DBLOG);
+    if (g_strcmp0(pref_dblog, "off") == 0) {
+        return FALSE;
+    }
+    if (g_strcmp0(pref_dblog, "redact") == 0) {
+        return FALSE;
+    }
+    return TRUE;
+}
+
 gboolean
 log_database_init(ProfAccount* account)
 {