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

A `go install` of a tag sets no linker flags, so the binary reported
`dev`. Version, commit and commit date that the linker flags leave
unset now come from the build info Go records. Go records a
pseudo-version for an untagged commit and a `+dirty` suffix for a
modified checkout; `IsDevVersion` now counts both as development
builds, using `golang.org/x/mod`.

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()