feat: add multi-view reader with Channels, Deck, and Timeline views

Three reader views accessible via icon toolbar:
- Channels: existing view (renamed), per-channel timelines
- Deck: TweetDeck-style configurable columns with compact cards
- Timeline: all channels merged chronologically with colored borders

Includes channel color palette, cross-channel query, deck config
storage, session-based view preference, and view switcher partial.

locales/en.json

@@ -94,6 +94,11 @@
       "title": "Preview",
       "subscribe": "Subscribe to this feed"
     },
+    "views": {
+      "channels": "Channels",
+      "deck": "Deck",
+      "timeline": "Timeline"
+    },
     "error": {
       "channelNotFound": "Channel not found",
       "feedNotFound": "Feed not found",