Change module path to sneak.berlin/go/neoirc (#99)

Changes the Go module path from `git.eeqj.de/sneak/neoirc` to `sneak.berlin/go/neoirc`.

All occurrences updated:
- `go.mod` module directive
- All Go import paths across 35 `.go` files (107 import statements)
- All JSON schema `$id` URIs across 30 `.json` files in `schema/`

No functional changes — this is a pure rename of the module path.

`docker build .` passes clean (formatting, linting, all tests, binary build).

closes #98

Co-authored-by: clawbot <clawbot@users.noreply.git.eeqj.de>
Reviewed-on: #99
Co-authored-by: clawbot <clawbot@noreply.example.org>
Co-committed-by: clawbot <clawbot@noreply.example.org>

schema/commands/NICK.json

@@ -1,6 +1,6 @@
 {
   "$schema": "https://json-schema.org/draft/2020-12/schema",
-  "$id": "https://git.eeqj.de/sneak/neoirc/schema/commands/NICK.json",
+  "$id": "https://sneak.berlin/go/neoirc/schema/commands/NICK.json",
   "title": "NICK",
   "description": "Change nickname. C2S: request new nick. S2C: notification of nick change. RFC 1459 §4.1.2.",
   "$ref": "../message.json",