feat: add IRCv3 cap negotiation, channel management, state persistence

Implement CAP LS 302 flow with configurable ircv3_caps list, replacing
the minimal SASL-only registration. Parse IRCv3 message tags (@key=value)
with proper value unescaping. Add channel management plugin (kick, ban,
unban, topic, mode) and bot API methods. Add SQLite key-value StateStore
for plugin state persistence with !state inspection command.

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

tests/test_plugin.py

@@ -6,6 +6,7 @@ from pathlib import Path
 from derp.bot import _AMBIGUOUS, Bot
 from derp.irc import Message
 from derp.plugin import PluginRegistry, command, event
+from derp.state import StateStore
 
 
 class TestDecorators:
@@ -445,11 +446,11 @@ class TestIsAdmin:
     def _msg(prefix: str) -> Message:
         """Create a minimal Message with a given prefix."""
         return Message(raw="", prefix=prefix, nick=prefix.split("!")[0],
-                       command="PRIVMSG", params=["#test", "!test"])
+                       command="PRIVMSG", params=["#test", "!test"], tags={})
 
     def test_no_prefix_not_admin(self):
         bot = self._make_bot()
-        msg = Message(raw="", prefix=None, nick=None, command="PRIVMSG", params=[])
+        msg = Message(raw="", prefix=None, nick=None, command="PRIVMSG", params=[], tags={})
         assert bot._is_admin(msg) is False
 
     def test_oper_is_admin(self):
@@ -476,3 +477,71 @@ class TestIsAdmin:
         bot = self._make_bot()
         msg = self._msg("nobody!~user@host")
         assert bot._is_admin(msg) is False
+
+
+class TestStateStore:
+    """Test the SQLite key-value state store."""
+
+    def test_get_missing_returns_default(self, tmp_path: Path):
+        store = StateStore(tmp_path / "state.db")
+        assert store.get("plug", "key") is None
+        assert store.get("plug", "key", "fallback") == "fallback"
+
+    def test_set_and_get(self, tmp_path: Path):
+        store = StateStore(tmp_path / "state.db")
+        store.set("plug", "color", "blue")
+        assert store.get("plug", "color") == "blue"
+
+    def test_set_overwrite(self, tmp_path: Path):
+        store = StateStore(tmp_path / "state.db")
+        store.set("plug", "val", "one")
+        store.set("plug", "val", "two")
+        assert store.get("plug", "val") == "two"
+
+    def test_namespace_isolation(self, tmp_path: Path):
+        store = StateStore(tmp_path / "state.db")
+        store.set("alpha", "key", "a")
+        store.set("beta", "key", "b")
+        assert store.get("alpha", "key") == "a"
+        assert store.get("beta", "key") == "b"
+
+    def test_delete_existing(self, tmp_path: Path):
+        store = StateStore(tmp_path / "state.db")
+        store.set("plug", "key", "val")
+        assert store.delete("plug", "key") is True
+        assert store.get("plug", "key") is None
+
+    def test_delete_missing(self, tmp_path: Path):
+        store = StateStore(tmp_path / "state.db")
+        assert store.delete("plug", "ghost") is False
+
+    def test_keys(self, tmp_path: Path):
+        store = StateStore(tmp_path / "state.db")
+        store.set("plug", "b", "2")
+        store.set("plug", "a", "1")
+        store.set("other", "c", "3")
+        assert store.keys("plug") == ["a", "b"]
+        assert store.keys("other") == ["c"]
+        assert store.keys("empty") == []
+
+    def test_clear(self, tmp_path: Path):
+        store = StateStore(tmp_path / "state.db")
+        store.set("plug", "a", "1")
+        store.set("plug", "b", "2")
+        store.set("other", "c", "3")
+        count = store.clear("plug")
+        assert count == 2
+        assert store.keys("plug") == []
+        assert store.keys("other") == ["c"]
+
+    def test_clear_empty(self, tmp_path: Path):
+        store = StateStore(tmp_path / "state.db")
+        assert store.clear("empty") == 0
+
+    def test_close_and_reopen(self, tmp_path: Path):
+        db_path = tmp_path / "state.db"
+        store = StateStore(db_path)
+        store.set("plug", "persist", "yes")
+        store.close()
+        store2 = StateStore(db_path)
+        assert store2.get("plug", "persist") == "yes"