Re-vendor the canonical files from sneak/prompts at dd4027b (closes #213)

Linting and testing become the lint and test phases of the Dockerfile,
and the build stage depends on both. Dockerfile.lint, CHECK_EPOCH and
the tests that checked them are removed. Every docker build in script/
passes --no-cache, and script/cibuild runs script/bootstrap first. The
image takes its version from the VERSION build arg or git describe, and
still stamps the commit and its date from .git. The golangci-lint
v2.14.0 findings are fixed in the code. The rules in CLAUDE.md move into
AGENTS.md. IsDevVersion now counts "unknown", the version script/docker
stamps outside a git checkout.

Model: opus-5-5

internal/globals/globals_test.go

@@ -74,6 +74,9 @@ func TestIsDevVersion(t *testing.T) {
 		// as one. The Makefile refuses to build when script/version
 		// yields nothing; this covers a binary linked some other way.
 		{"", true},
+		// What script/docker and script/cibuild stamp when the host
+		// has no git checkout.
+		{"unknown", true},
 	}
 
 	for _, tc := range cases {