Customizable nav lanes: pin moods / topics / discovery tags

Readers can now choose which quick-access lanes sit above the feed; "Today"
stays pinned. The pool (goodnews/lanes.py, served at /api/lanes) is one source
of truth over three lane kinds the feed already renders: moods, primary topics,
and high-volume Discovery tags. Selection lives in the existing prefs blob
(localStorage + /api/prefs sync); the filter parser ignores the new `lanes`
field, so it rides along harmlessly. Default = today's moods, unchanged.

Food/Space stay grouping tags rather than primary topics (per review): `space`
already existed; added `food` to the Mind & Craft family so the classifier
assigns it, and seeded the Food lane by re-tagging the two food sources.

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

goodnews/taxonomy.py

@@ -40,7 +40,7 @@ FAMILIES: dict[str, dict] = {
     },
     "Mind & Craft": {
         "description": "Ideas, learning, and making.",
-        "tags": ["learning", "ideas", "arts", "books", "creativity", "perspective", "work-life"],
+        "tags": ["learning", "ideas", "arts", "books", "creativity", "perspective", "work-life", "food"],
     },
 }