Rename app from chat to neoirc, binary to neoircd (closes #46)

- Rename Go module path: git.eeqj.de/sneak/chat -> git.eeqj.de/sneak/neoirc
- Rename binary: chatd -> neoircd, chat-cli -> neoirc-cli
- Rename cmd directories: cmd/chatd -> cmd/neoircd, cmd/chat-cli -> cmd/neoirc-cli
- Rename Go package: chatapi -> neoircapi
- Update Makefile: binary name, build targets, docker image tag, clean target
- Update Dockerfile: binary paths, user/group names, ENTRYPOINT
- Update .gitignore and .dockerignore
- Update all Go imports and doc comments
- Update default server name fallback: chat -> neoirc
- Update web client: localStorage keys, page title, default server name
- Update all schema $id URLs and example hostnames
- Update README.md: project name, binary references, examples, directory tree
- Update AGENTS.md: build command reference
- Update test fixtures: app name and channel names

schema/message.json

@@ -1,6 +1,6 @@
 {
   "$schema": "https://json-schema.org/draft/2020-12/schema",
-  "$id": "https://git.eeqj.de/sneak/chat/schema/message.json",
+  "$id": "https://git.eeqj.de/sneak/neoirc/schema/message.json",
   "title": "IRC Message Envelope",
   "description": "Base envelope for all messages. Mirrors IRC wire format (RFC 1459/2812) encoded as JSON over HTTP. The 'command' field carries either an IRC command name (PRIVMSG, JOIN, etc.) or a three-digit numeric reply code (001, 353, 433, etc.).",
   "type": "object",