feat: metadata enrichment for alerts and subscription plugins

Alert backends now populate structured `extra` field with engagement
metrics (views, stars, votes, etc.) instead of embedding them in titles.
Subscription plugins show richer announcements: Twitch viewer counts,
YouTube views/likes/dates, RSS published dates.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

tests/test_rss.py

@@ -25,6 +25,7 @@ from plugins.rss import (  # noqa: E402
     _feeds,
     _load,
     _parse_atom,
+    _parse_date,
     _parse_feed,
     _parse_rss,
     _poll_once,
@@ -52,16 +53,19 @@ RSS_FEED = b"""\
       <guid>item-1</guid>
       <title>First Post</title>
       <link>https://example.com/1</link>
+      <pubDate>Mon, 10 Feb 2026 09:00:00 +0000</pubDate>
     </item>
     <item>
       <guid>item-2</guid>
       <title>Second Post</title>
       <link>https://example.com/2</link>
+      <pubDate>Tue, 11 Feb 2026 14:30:00 +0000</pubDate>
     </item>
     <item>
       <guid>item-3</guid>
       <title>Third Post</title>
       <link>https://example.com/3</link>
+      <pubDate>Wed, 12 Feb 2026 08:00:00 +0000</pubDate>
     </item>
   </channel>
 </rss>
@@ -88,11 +92,13 @@ ATOM_FEED = b"""\
     <id>atom-1</id>
     <title>Atom First</title>
     <link href="https://example.com/a1"/>
+    <published>2026-02-15T10:00:00Z</published>
   </entry>
   <entry>
     <id>atom-2</id>
     <title>Atom Second</title>
     <link href="https://example.com/a2"/>
+    <published>2026-02-16T15:30:00Z</published>
   </entry>
 </feed>
 """
@@ -333,6 +339,20 @@ class TestParseRSS:
         assert items[0]["title"] == "First Post"
         assert items[0]["link"] == "https://example.com/1"
 
+    def test_parses_pubdate(self):
+        import xml.etree.ElementTree as ET
+        root = ET.fromstring(RSS_FEED)
+        _, items = _parse_rss(root)
+        assert items[0]["date"] == "2026-02-10"
+        assert items[1]["date"] == "2026-02-11"
+        assert items[2]["date"] == "2026-02-12"
+
+    def test_no_pubdate_empty_string(self):
+        import xml.etree.ElementTree as ET
+        root = ET.fromstring(RSS_NO_GUID)
+        _, items = _parse_rss(root)
+        assert items[0]["date"] == ""
+
     def test_fallback_to_link_as_id(self):
         import xml.etree.ElementTree as ET
         root = ET.fromstring(RSS_NO_GUID)
@@ -364,6 +384,19 @@ class TestParseAtom:
         assert items[0]["title"] == "Atom First"
         assert items[0]["link"] == "https://example.com/a1"
 
+    def test_parses_published_date(self):
+        import xml.etree.ElementTree as ET
+        root = ET.fromstring(ATOM_FEED)
+        _, items = _parse_atom(root)
+        assert items[0]["date"] == "2026-02-15"
+        assert items[1]["date"] == "2026-02-16"
+
+    def test_no_published_empty_string(self):
+        import xml.etree.ElementTree as ET
+        root = ET.fromstring(ATOM_NO_ID)
+        _, items = _parse_atom(root)
+        assert items[0]["date"] == ""
+
     def test_fallback_to_link_as_id(self):
         import xml.etree.ElementTree as ET
         root = ET.fromstring(ATOM_NO_ID)
@@ -755,6 +788,9 @@ class TestCmdRssCheck:
             assert len(announcements) == 2
             assert "[news]" in announcements[0]
             assert "Second Post" in announcements[0]
+            # Verify date suffix
+            assert "| 2026-02-11" in announcements[0]
+            assert "| 2026-02-12" in announcements[1]
 
         asyncio.run(inner())
 
@@ -1073,3 +1109,27 @@ class TestCmdRssUsage:
         bot = _FakeBot()
         asyncio.run(cmd_rss(bot, _msg("!rss foobar")))
         assert "Usage:" in bot.replied[0]
+
+
+# ---------------------------------------------------------------------------
+# TestParseDate
+# ---------------------------------------------------------------------------
+
+class TestParseDate:
+    def test_iso_format(self):
+        assert _parse_date("2026-02-15T10:00:00Z") == "2026-02-15"
+
+    def test_iso_with_offset(self):
+        assert _parse_date("2026-02-15T10:00:00+00:00") == "2026-02-15"
+
+    def test_rfc2822_format(self):
+        assert _parse_date("Mon, 10 Feb 2026 09:00:00 +0000") == "2026-02-10"
+
+    def test_empty_string(self):
+        assert _parse_date("") == ""
+
+    def test_garbage(self):
+        assert _parse_date("not a date") == ""
+
+    def test_date_only(self):
+        assert _parse_date("2026-01-01") == "2026-01-01"