feat(entries): multiline Notes field for any entry, masked by default

The note body of a note entry is the encrypted_password column, so logins had no way to carry notes. Rather than a dedicated encrypted column and the seven call sites that come with it, this rides on custom_fields, which rotation, duplicate, export/import and sync already carry.

Both the open-time normalisation and the save-time rebuild drop any key they do not name, so multiline is carried explicitly in each - otherwise the field silently reopens single-line.

css/style.css

@@ -1601,6 +1601,15 @@ input[type="range"]::-webkit-slider-thumb {
     padding: 4px 8px;
     font-size: 12px;
 }
+/* Multiline custom field (Notes). The row stays a grid, so the textarea just
+   grows in its own column and the buttons keep their places. */
+.so-custom-multiline {
+    min-height: 72px;
+    resize: vertical;
+    align-self: stretch;
+    font-family: inherit;
+    line-height: 1.5;
+}
 /* Editable combobox for option-backed custom fields (card brand, expiry
    year…). Input fills the cell; the arrow drops a menu of ALL options. */
 .so-combo { position: relative; display: flex; align-items: center; }
@@ -1875,7 +1884,8 @@ input[type="range"]::-webkit-slider-thumb {
 }
 /* A textarea has no type="password"; -webkit-text-security is the Chromium
    equivalent (WebView2 is Chromium, so it's always available here). */
-.so-note-body.is-masked { -webkit-text-security: disc; }
+.so-note-body.is-masked,
+.so-custom-multiline.is-masked { -webkit-text-security: disc; }
 .so-note-label { display: flex; align-items: center; justify-content: space-between; }
 
 /* ---- + New dropdown ---------------------------------- */