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/lanes.py

@@ -18,8 +18,12 @@ from __future__ import annotations
 from .moods import MOODS
 from .taxonomy import ALLOWED_TAGS, TOPICS
 
-# The lane pinned first, always — never user-removable.
-PINNED = {"key": "today", "label": "Today", "description": "The day's good things."}
+# The lanes pinned first, always — never user-removable. "Highlights" is the
+# curated daily brief (key 'today'); "Latest" is the chronological accepted feed.
+PINNED = [
+    {"key": "today", "label": "Highlights", "description": "The day's curated good things."},
+    {"key": "latest", "label": "Latest", "description": "Freshest calm reads, newest first."},
+]
 
 # What a reader who has never customized sees: today's curated moods, unchanged.
 DEFAULT_LANES: list[str] = [m["key"] for m in MOODS if m["key"] != "today"]