Make the tagged-release path work on Gitea (closes #65)

No tag could be cut at all: .goreleaser.yaml had no gitea_urls block, so
goreleaser defaulted to the GitHub API, and the repo has zero tags.

.goreleaser.yaml now points at git.eeqj.de. Version derives from git via
a new script/version - exact tag with any leading v stripped, else
dev-<12-char sha>, with a -dirty suffix when tracked files are modified -
replacing the hardcoded 1.0.0-rc.1 that every local build was stamping
regardless of git state. A tag-triggered .gitea/workflows/release.yml
runs goreleaser with a scoped token (RELEASE_TOKEN); script/bootstrap
installs a sha256-verified goreleaser, and make release / release-snapshot
become script shims like every other target.

Two fabrications were removed rather than merely replaced. goreleaser's
snapshot.version_template was `{{ incpatch .Version }}-next`, which
invents a release number from the last tag - and with no tags, from
goreleaser's own fabricated v0.0.0. And internal/cli/version.go gated its
development-build notice on Version == "dev" exactly, so the moment
untagged builds carried a sha that notice would have gone silent and an
unreleased binary would have read as a release. Replaced with a tested
IsDevVersion predicate, and closed at both layers: the Makefile now
refuses to build when script/version yields nothing, and an empty version
counts as a development build - reachable today via
`docker build --build-arg VERSION=`.

The release workflow installs Go from a sha-pinned actions/setup-go
(v5.6.0) using go-version-file, so the compiler that produces released
binaries is pinned like every other external reference. Without it the
first tag push would either fail at goreleaser's before-hook or compile
the published artifacts with whatever unpinned Go the runner happened to
carry - the one unpinned thing in a release path that already refuses an
unpinned goreleaser.

Known gap: the Go tarball setup-go fetches is version-pinned but not
checksum-verified against a value in this repo, unlike the goreleaser
install and the Dockerfile digest.

internal/globals/globals.go

@@ -3,14 +3,23 @@
 package globals
 
 import (
+	"strings"
 	"time"
 )
 
 // Appname is the application name, populated from main().
 var Appname = "vaultik" //nolint:gochecknoglobals // set via -ldflags at build time
 
+// DevVersion is the version a binary reports when it was not built
+// from a tagged commit. script/version emits either this exact string
+// (outside a git checkout) or this string followed by "-" and the
+// commit it was built from, and goreleaser's snapshot template matches
+// that shape. It is deliberately not a number: a build that is not a
+// release must not name itself like one.
+const DevVersion = "dev"
+
 // Version is the application version, populated from main().
-var Version = "dev" //nolint:gochecknoglobals // set via -ldflags at build time
+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
@@ -24,6 +33,9 @@ const Author = "Jeffrey Paul <sneak@sneak.berlin>"
 // Homepage is the canonical URL for vaultik.
 const Homepage = "https://sneak.berlin/go/vaultik"
 
+// ReleasesURL is where tagged release artifacts are published.
+const ReleasesURL = "https://git.eeqj.de/sneak/vaultik/releases"
+
 // License is the SPDX identifier for the project license.
 const License = "MIT"
 
@@ -47,6 +59,21 @@ func New() (*Globals, error) {
 	}, nil
 }
 
+// IsDevVersion reports whether v names a development build rather than
+// a release. Both "dev" and "dev-<sha>" (and its "-dirty" variant)
+// count: a caller that compares against "dev" exactly would treat every
+// commit-stamped development build as a release.
+//
+// The empty string counts too. Nothing that knows its version reports
+// no version, so an empty Version means the stamping failed, and the
+// 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.
+func IsDevVersion(v string) bool {
+	return v == "" || v == DevVersion || strings.HasPrefix(v, DevVersion+"-")
+}
+
 // shortCommitLen is the number of commit-hash characters ShortCommit keeps.
 const shortCommitLen = 12