Add a permanent "Latest" lane beside "Highlights"

Restructure the nav around two permanent lanes, then the reader's chosen ones:
"Highlights" (the curated daily brief — formerly "Today") and "Latest" (the
freshest accepted stories, newest-first). Now that the gate is tight, a
chronological "incoming" feed is safe to expose.

* feed(): new sort="latest" (pure recency) alongside the default best-first
  rank; /api/feed exposes sort=ranked|latest (validated). Still accepted-only
  and boundary-respecting either way.
* lanes.py: two pinned lanes (Highlights + Latest) instead of one.
* Home: "Latest" view + "Load more" pagination for every feed view (offset-
  paged, de-duped). Mobile bottom bar gains a Latest tab.
* LanePicker shows both pinned lanes; nav rail renders them first.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

goodnews/api.py

@@ -921,6 +921,7 @@ def create_app() -> FastAPI:
         prefs: str | None = Query(None),
         exclude: str = Query("", description="comma-separated article ids the reader has dismissed"),
         tag: str | None = Query(None, description="grouping tag to browse"),
+        sort: str = Query("ranked", pattern="^(ranked|latest)$", description="ranked (best-first) or latest (newest-first)"),
     ) -> FeedResponse:
         if topic and topic.lower() not in TOPICS:
             raise HTTPException(400, f"unknown topic: {topic}")
@@ -939,14 +940,14 @@ def create_app() -> FastAPI:
                 fetch_n = min(2000, (offset + limit) * 4 + 50 + len(excl))
                 raw = queries.feed(
                     conn, topic=topic, flavor=flavor, accepted_only=accepted_only,
-                    limit=fetch_n, offset=0, tag=tag, **kw,
+                    limit=fetch_n, offset=0, tag=tag, sort=sort, **kw,
                 )
                 kept = [a for a in filter_articles(raw, fp, now) if a["id"] not in excl]
                 rows = kept[offset : offset + limit]
             else:
                 rows = queries.feed(
                     conn, topic=topic, flavor=flavor, accepted_only=accepted_only,
-                    limit=limit, offset=offset, tag=tag, **kw,
+                    limit=limit, offset=offset, tag=tag, sort=sort, **kw,
                 )
         # Keep the top of a browse view readable: stable-sort paywalled items
         # below readable ones (composite order preserved within each group).