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/commands/TOPIC.json

@@ -1,6 +1,6 @@
 {
   "$schema": "https://json-schema.org/draft/2020-12/schema",
-  "$id": "https://git.eeqj.de/sneak/chat/schema/commands/TOPIC.json",
+  "$id": "https://git.eeqj.de/sneak/neoirc/schema/commands/TOPIC.json",
   "title": "TOPIC",
   "description": "Get or set channel topic. C2S: set topic (body present) or query (body absent). S2C: topic change notification. RFC 1459 §4.2.4.",
   "$ref": "../message.json",
@@ -17,6 +17,6 @@
   },
   "required": ["command", "to"],
   "examples": [
-    { "command": "TOPIC", "from": "alice", "to": "#general", "body": ["Welcome to the chat"] }
+    { "command": "TOPIC", "from": "alice", "to": "#general", "body": ["Welcome to the channel"] }
   ]
 }