feat: add setting to disable tag-color row tint in message list

Message-list rows are tinted with the first tag's color, which becomes
overwhelming when a label applies to most messages (for example
per-account labels). Add a `tintListRowsByTag` setting (default true, so
current behavior is unchanged) with a toggle in Settings beside
"Colorful Sidebar Icons". When off, rows are not tinted; tag dots and
chips still show the color. Gated in both list renderers
(email-list-item and thread-list-item).

locales/en/common.json

@@ -941,6 +941,10 @@
         "label": "Colorful Sidebar Icons",
         "description": "Tint folder and tag icons by type (blue Inbox, red Junk, green Sent, etc.). Disable for a monochrome sidebar."
       },
+      "tint_list_rows": {
+        "label": "Tint List Rows by Tag Color",
+        "description": "Shade each message row with its first tag color. Disable to keep rows plain; tag dots and chips still show the color."
+      },
       "show_folder_total_count": {
         "label": "Show Total Message Count",
         "description": "Show the total message count next to folders and tags, alongside the unread count. Disable to show only unread counts."