Re-vendor the canonical files from sneak/prompts at dd4027b (closes #112)

The shared files are fetched from sneak/prompts dd4027b, with this
repository's own entries after the shared content in .gitignore,
.editorconfig and .dockerignore.

Lint and tests are Dockerfile phases (golangci-lint v2.14.0, Debian Go
1.24.13) that the build stage depends on, and the Makefile targets call
the script/ entrypoints. make fmt also formats Markdown with prettier.

Fixes for the new lint findings: the auth cookie is always Secure, an
IRC connection's relay goroutine stops when the connection closes, and
repeated strings are constants.

Model: opus-5-5

AGENTS.md

@@ -2,10 +2,12 @@
 
 ## Before Every Commit
 
-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/neoircd` — compiles clean
+1. **Format**: `make fmt`
+2. **Check**: `make check` — the tests and the linter, which run in Docker, and
+   the format check: all passing, zero issues
+
+Never run `go test`, `golangci-lint` or `gofmt` directly; use the `make`
+targets.
 
 No commit lands on main with lint errors, test failures, or formatting issues.