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. A
host without Go gets the go.mod version from script/install-go in
.tool/go, which bootstrap, the Makefile, fmt, fmt-check, precommit and
release add to PATH; fmt-check skips .tool. The image takes its version
from the VERSION build arg or git describe, dev without .git. This
repo's own entries follow the canonical content in .gitignore and
.editorconfig. The golangci-lint v2.14.0 findings are fixed. The rules
in CLAUDE.md move into AGENTS.md. IsDevVersion counts "unknown".

Model: opus-5-5

internal/globals/globals.go

@@ -18,14 +18,19 @@ var Appname = "vaultik" //nolint:gochecknoglobals // set via -ldflags at build t
 // deliberately not a number.
 const DevVersion = "dev"
 
+// Unknown is what Commit and CommitDate hold when the build did not
+// stamp them, and the version script/docker and script/cibuild stamp
+// when the host has no git checkout.
+const Unknown = "unknown"
+
 // Version is the application version, populated from main().
 var Version = DevVersion //nolint:gochecknoglobals // set via -ldflags at build time
 
 // Commit is the git commit hash, populated from main().
-var Commit = "unknown" //nolint:gochecknoglobals // set via -ldflags at build time
+var Commit = Unknown //nolint:gochecknoglobals // set via -ldflags at build time
 
 // CommitDate is the ISO-8601 date of the commit, populated from main().
-var CommitDate = "unknown" //nolint:gochecknoglobals // set via -ldflags at build time
+var CommitDate = Unknown //nolint:gochecknoglobals // set via -ldflags at build time
 
 // Author identifies the upstream author of vaultik.
 const Author = "Jeffrey Paul <sneak@sneak.berlin>"
@@ -72,9 +77,11 @@ func New() (*Globals, error) {
 // safe reading of "we could not establish that this is a release" is
 // that it is not one. The Makefile refuses to build at all in that
 // case; this is the second line of defence, for a binary linked by
-// something other than the Makefile.
+// something other than the Makefile. Unknown counts for the same
+// reason.
 func IsDevVersion(v string) bool {
-	if v == "" || v == DevVersion || strings.HasPrefix(v, DevVersion+"-") ||
+	if v == "" || v == Unknown || v == DevVersion ||
+		strings.HasPrefix(v, DevVersion+"-") ||
 		strings.HasSuffix(v, "-dirty") {
 		return true
 	}

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 {