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

AGENTS.md

@@ -5,7 +5,7 @@
 1. **Format**: `gofmt -s -w .` and `goimports -w .`
 2. **Lint**: `golangci-lint run --config .golangci.yml ./...` — zero issues
 3. **Test**: `go test -race ./...` — all passing
-4. **Build**: `go build ./cmd/chatd` — compiles clean
+4. **Build**: `go build ./cmd/neoircd` — compiles clean
 
 No commit lands on main with lint errors, test failures, or formatting issues.