Report the Go build info version when linker flags set none (closes #422)

A binary from go install, the README's first command, reported itself as version dev, a development build, although Go had recorded the tag it was built from. When the linker flags leave the version, commit or commit date unset, they are now filled in from the Go build info, so such a binary reports its tag and counts as a release. Builds through make, script/docker and goreleaser are unchanged.

Model: opus-5-5

internal/cli/entry.go

@@ -21,6 +21,8 @@ const shortCommitLen = 12
 const exitCodeInterrupted = 130
 
 // Entry is the main entry point for the CLI application.
+// It first calls globals.FillUnsetFromBuildInfo, which fills in the
+// version, commit and commit date that the linker flags did not set.
 // It prints the startup banner to stderr (unless a banner-suppressing
 // flag is present in os.Args — see bannerSuppressedInArgs), executes the
 // root cobra command, and routes any returned error through the
@@ -33,6 +35,7 @@ const exitCodeInterrupted = 130
 // deferred profile writers run before the process ends. See run in
 // cmd/vaultik/main.go.
 func Entry() int {
+	globals.FillUnsetFromBuildInfo()
 	emitStartupBanner(os.Args[1:], os.Stderr)
 
 	rootCmd := NewRootCommand()