feat: mode-aware subreddit color overrides with v1→v2 migration

Co-authored-by: Cursor <cursoragent@cursor.com>

lib/settings.js

@@ -19,10 +19,29 @@
     subredditColors: {},
   };
 
+  function migrateSubredditColors(colors) {
+    let migrated = false;
+    const result = {};
+    for (const name of Object.keys(colors)) {
+      const entry = colors[name];
+      if (entry && entry.bg !== undefined && !entry.light && !entry.dark) {
+        result[name] = { light: { bg: entry.bg, border: entry.border, text: entry.text }, dark: { bg: entry.bg, border: entry.border, text: entry.text } };
+        migrated = true;
+      } else {
+        result[name] = entry;
+      }
+    }
+    return { result: result, migrated: migrated };
+  }
+
   async function loadSettings() {
     const stored = await browser.storage.local.get(null);
     const merged = Object.assign({}, DEFAULTS, stored);
-    merged.subredditColors = Object.assign({}, merged.subredditColors);
+    const migration = migrateSubredditColors(merged.subredditColors || {});
+    merged.subredditColors = migration.result;
+    if (migration.migrated) {
+      await browser.storage.local.set({ subredditColors: merged.subredditColors });
+    }
     return merged;
   }