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>

README.md

@@ -22,7 +22,7 @@ make down      # Stop
 
 ## Features
 
-- Async IRC over plain TCP or TLS (SASL PLAIN auth)
+- Async IRC over plain TCP or TLS (SASL PLAIN auth, IRCv3 CAP negotiation)
 - Plugin system with `@command` and `@event` decorators
 - Hot-reload: load, unload, reload plugins at runtime
 - Admin permission system (hostmask patterns + IRCOP detection)
@@ -35,7 +35,7 @@ make down      # Stop
 
 | Plugin | Commands | Description |
 |--------|----------|-------------|
-| core | ping, help, version, uptime, whoami, admins, load, reload, unload, plugins | Bot management |
+| core | ping, help, version, uptime, whoami, admins, load, reload, unload, plugins, state | Bot management |
 | dns | dns | Raw UDP DNS resolver (A/AAAA/MX/NS/TXT/CNAME/PTR/SOA) |
 | encode | encode, decode | Base64, hex, URL, ROT13 |
 | hash | hash, hashid | Hash generation + type identification |
@@ -61,6 +61,7 @@ make down      # Stop
 | headers | headers | HTTP header fingerprinting |
 | exploitdb | exploitdb | Exploit-DB search (local CSV) |
 | payload | payload | SQLi/XSS/SSTI/LFI/CMDi/XXE templates |
+| chanmgmt | kick, ban, unban, topic, mode | Channel management (admin) |
 | example | echo | Demo plugin |
 
 ## Writing Plugins