SEO flywheel: /today digest, sitemap, robots, home OG tags

Make the summary pages discoverable so traffic compounds passively:
- /today: a server-rendered, shareable + indexable digest of today's brief —
  each item's title (→ /a summary), our summary, and a source link. OG/Twitter
  meta + self-canonical.
- /sitemap.xml: dynamic — home, /today, and every accepted non-duplicate /a page
  with lastmod. robots.txt allows all and points to it.
- Home (SPA shell) gains canonical + OG/Twitter tags for cleaner unfurls.
- Caddy routes /today + /sitemap.xml to the API. 133 tests pass.

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

tests/test_seo.py

@@ -0,0 +1,45 @@
+import pytest
+from fastapi.testclient import TestClient
+
+
+@pytest.fixture
+def client(tmp_path, monkeypatch):
+    db = tmp_path / "t.sqlite3"
+    monkeypatch.setenv("GOODNEWS_DB", str(db))
+    monkeypatch.setenv("GOODNEWS_PUBLIC_BASE_URL", "https://upbeatbytes.com")
+    import importlib
+    import goodnews.api as api
+    importlib.reload(api)
+    from goodnews.db import connect, init_db
+    c = connect(str(db)); init_db(c)
+    c.execute("INSERT INTO sources (id,name,feed_url,trust_score) VALUES (1,'BBC','http://s/f',5)")
+    c.execute("INSERT INTO articles (id,source_id,canonical_url,title,url_hash,published_at) "
+              "VALUES (1,1,'https://bbc.com/x','Bees are back','h1','2026-06-05T08:00:00')")
+    c.execute("INSERT INTO article_scores (article_id,accepted,reason_text) VALUES (1,1,'Hopeful.')")
+    c.execute("INSERT INTO article_summaries (article_id,summary) VALUES (1,'Bee numbers recovered after a restoration effort.')")
+    c.execute("INSERT INTO daily_briefs (id,brief_date,title) VALUES (1,'2026-06-05','B')")
+    c.execute("INSERT INTO daily_brief_items (brief_id,article_id,rank) VALUES (1,1,1)")
+    c.commit(); c.close()
+    return api.create_app()
+
+
+def test_today_digest(client):
+    r = TestClient(client).get("/today")
+    assert r.status_code == 200
+    html = r.text
+    assert "Bees are back" in html
+    assert "Bee numbers recovered" in html              # our summary
+    assert 'href="/a/1"' in html and "bbc.com/x" in html  # summary + source links
+    assert 'rel="canonical" href="https://upbeatbytes.com/today"' in html
+    assert 'property="og:title"' in html
+
+
+def test_sitemap(client):
+    r = TestClient(client).get("/sitemap.xml")
+    assert r.status_code == 200
+    assert "application/xml" in r.headers["content-type"]
+    xml = r.text
+    assert "<urlset" in xml
+    assert "https://upbeatbytes.com/a/1" in xml
+    assert "https://upbeatbytes.com/today" in xml
+    assert "<lastmod>2026-06-05</lastmod>" in xml