Rename app from chat to neoirc, binary to neoircd (closes #46) (#47)

Complete rename of the application from `chat` to `neoirc` with binary name `neoircd`.

closes #46

## Changes

- **Go module path**: `git.eeqj.de/sneak/chat` → `git.eeqj.de/sneak/neoirc`
- **Server binary**: `chatd` → `neoircd`
- **CLI binary**: `chat-cli` → `neoirc-cli`
- **Cmd directories**: `cmd/chatd` → `cmd/neoircd`, `cmd/chat-cli` → `cmd/neoirc-cli`
- **Go package**: `chatapi` → `neoircapi`
- **Makefile**: binary name, build targets, docker image tag, clean target
- **Dockerfile**: binary paths, user/group names (`chat` → `neoirc`), ENTRYPOINT
- **`.gitignore`/`.dockerignore`**: artifact names
- **All Go imports and doc comments**
- **Default server name**: `chat` → `neoirc`
- **Web client**: localStorage keys (`chat_token`/`chat_channels` → `neoirc_token`/`neoirc_channels`), page title, default server display name
- **Schema files**: all `$id` URLs and example hostnames
- **README.md**: project name, all binary references, examples, directory tree
- **AGENTS.md**: build command reference
- **Test fixtures**: app name and channel names

Docker build passes. All tests pass.

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Co-authored-by: clawbot <clawbot@noreply.eeqj.de>
Reviewed-on: #47
Co-authored-by: clawbot <clawbot@noreply.example.org>
Co-committed-by: clawbot <clawbot@noreply.example.org>

schema/commands/PART.json

@@ -1,6 +1,6 @@
 {
   "$schema": "https://json-schema.org/draft/2020-12/schema",
-  "$id": "https://git.eeqj.de/sneak/chat/schema/commands/PART.json",
+  "$id": "https://git.eeqj.de/sneak/neoirc/schema/commands/PART.json",
   "title": "PART",
   "description": "Leave a channel. C2S: request to leave. S2C: notification that a user left. RFC 1459 §4.2.2.",
   "$ref": "../message.json",