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_youtube.py

@@ -19,6 +19,7 @@ _spec.loader.exec_module(_mod)
 from plugins.youtube import (  # noqa: E402
     _MAX_ANNOUNCE,
     _channels,
+    _compact_num,
     _delete,
     _derive_name,
     _errors,
@@ -44,26 +45,48 @@ from plugins.youtube import (  # noqa: E402
 YT_ATOM_FEED = b"""\
 <?xml version="1.0" encoding="UTF-8"?>
 <feed xmlns:yt="http://www.youtube.com/xml/schemas/2015"
-      xmlns="http://www.w3.org/2005/Atom">
+      xmlns="http://www.w3.org/2005/Atom"
+      xmlns:media="http://search.yahoo.com/mrss/">
   <title>3Blue1Brown - Videos</title>
   <author><name>3Blue1Brown</name></author>
   <entry>
     <id>yt:video:abc123</id>
     <yt:videoId>abc123</yt:videoId>
     <title>Linear Algebra</title>
+    <published>2026-01-15T12:00:00+00:00</published>
     <link rel="alternate" href="https://www.youtube.com/watch?v=abc123"/>
+    <media:group>
+      <media:community>
+        <media:statistics views="1500000"/>
+        <media:starRating count="45000"/>
+      </media:community>
+    </media:group>
   </entry>
   <entry>
     <id>yt:video:def456</id>
     <yt:videoId>def456</yt:videoId>
     <title>Calculus</title>
+    <published>2026-02-01T08:30:00+00:00</published>
     <link rel="alternate" href="https://www.youtube.com/watch?v=def456"/>
+    <media:group>
+      <media:community>
+        <media:statistics views="820000"/>
+        <media:starRating count="32000"/>
+      </media:community>
+    </media:group>
   </entry>
   <entry>
     <id>yt:video:ghi789</id>
     <yt:videoId>ghi789</yt:videoId>
     <title>Neural Networks</title>
+    <published>2026-02-10T14:00:00+00:00</published>
     <link rel="alternate" href="https://www.youtube.com/watch?v=ghi789"/>
+    <media:group>
+      <media:community>
+        <media:statistics views="250000"/>
+        <media:starRating count="12000"/>
+      </media:community>
+    </media:group>
   </entry>
 </feed>
 """
@@ -362,6 +385,28 @@ class TestParseFeed:
         channel_name, _ = _parse_feed(YT_ATOM_FEED)
         assert channel_name == "3Blue1Brown"
 
+    def test_parses_published_date(self):
+        _, items = _parse_feed(YT_ATOM_FEED)
+        assert items[0]["date"] == "2026-01-15"
+        assert items[1]["date"] == "2026-02-01"
+        assert items[2]["date"] == "2026-02-10"
+
+    def test_parses_views(self):
+        _, items = _parse_feed(YT_ATOM_FEED)
+        assert items[0]["views"] == 1500000
+        assert items[1]["views"] == 820000
+
+    def test_parses_likes(self):
+        _, items = _parse_feed(YT_ATOM_FEED)
+        assert items[0]["likes"] == 45000
+        assert items[1]["likes"] == 32000
+
+    def test_no_media_defaults_zero(self):
+        _, items = _parse_feed(YT_ATOM_NO_VIDEOID)
+        assert items[0]["views"] == 0
+        assert items[0]["likes"] == 0
+        assert items[0]["date"] == ""
+
 
 # ---------------------------------------------------------------------------
 # TestResolveChannel
@@ -789,6 +834,11 @@ class TestCmdYtCheck:
             assert len(announcements) == 2
             assert "[news]" in announcements[0]
             assert "Calculus" in announcements[0]
+            # Verify metadata suffix (views, likes, date)
+            assert "| " in announcements[0]
+            assert "820kv" in announcements[0]
+            assert "32klk" in announcements[0]
+            assert "2026-02-01" in announcements[0]
 
         asyncio.run(inner())
 
@@ -1103,3 +1153,27 @@ class TestCmdYtUsage:
         bot = _FakeBot()
         asyncio.run(cmd_yt(bot, _msg("!yt foobar")))
         assert "Usage:" in bot.replied[0]
+
+
+# ---------------------------------------------------------------------------
+# TestCompactNum
+# ---------------------------------------------------------------------------
+
+class TestCompactNum:
+    def test_zero(self):
+        assert _compact_num(0) == "0"
+
+    def test_small(self):
+        assert _compact_num(999) == "999"
+
+    def test_one_k(self):
+        assert _compact_num(1000) == "1k"
+
+    def test_fractional_k(self):
+        assert _compact_num(1500) == "1.5k"
+
+    def test_one_m(self):
+        assert _compact_num(1_000_000) == "1M"
+
+    def test_fractional_m(self):
+        assert _compact_num(2_500_000) == "2.5M"