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

No tag could be cut from this repo at all. Three independent blockers.

goreleaser was configured for GitHub while the repo lives on Gitea:
.goreleaser.yaml had a release: block but no gitea_urls:, so goreleaser
defaulted to the GitHub API and a release would have failed or published
somewhere nobody is looking. It now points at https://git.eeqj.de/api/v1.

The version was a hardcoded Makefile constant, VERSION := 1.0.0-rc.1, so
every local build claimed to be a release candidate that had never been
tagged and did not exist, while git tag -l was empty and internal/globals
defaulted to dev. The version now comes from git, via the new
script/version: the exact tag with a leading v stripped when HEAD is on
one (so a make build and a goreleaser build of the same commit report the
same string, and it matches the archive names), otherwise dev-<12-char
sha>, with -dirty appended in either case when tracked files are
modified. Untracked files are not counted, matching git describe --dirty.
goreleaser's snapshot template gets the same treatment: it was
{{ incpatch .Version }}-next, which manufactures a release number from
the last tag and, with no tags at all, from goreleaser's fabricated
v0.0.0.

That change had one non-obvious consequence. internal/cli/version.go
gated its "this is a development build" notice on the version being
exactly "dev", so as soon as untagged builds carried a commit sha the
notice would have gone silent and an unreleased binary would have read as
a release. The gate is now globals.IsDevVersion, a predicate over a
string rather than a comparison against a global so that it can be
tested, and it is tested at the boundary that matters: dev-<sha> and its
-dirty variant are development builds, 1.0.0-dev and 1.0.0-rc.1 are not.
The command writes to cmd.OutOrStdout() so its output can be asserted on
at all.

Releases now come from CI rather than a workstation: a tag-triggered
.gitea/workflows/release.yml, with fetch-depth: 0 because a shallow
checkout has no tags and would silently mislabel the release, and with
the RELEASE_TOKEN repository secret passed as GITEA_TOKEN (documented in
README.md; the runner's automatic token is deliberately not used, since
it is not guaranteed to carry release write scope). script/release unsets
any GITHUB_TOKEN or GITLAB_TOKEN it finds, because goreleaser picks its
forge from whichever token variable is set and refuses to run when it
sees more than one -- an unrelated runner token must not get to decide
where these artifacts are published.

make release and make release-snapshot were the last two Makefile targets
that were not shims; they now call script/release and
script/release-snapshot, which resolve goreleaser the way script/lint
resolves the linter -- a PATH binary is accepted only at the pinned
version, never as a silent fallback. script/bootstrap installs it from a
sha256-verified GitHub release archive per REPO_POLICIES.md, through a
separate script/install-goreleaser: separate because script/bootstrap
hard-fails without a usable Docker daemon by design, and the release
runner needs goreleaser without needing Docker. dist/ and .tool/ are
gitignored and excluded from the Docker build context.

The release workflow installs its own Go toolchain, pinned. goreleaser
is not a compiler: it shells out to go for the before: hook and for all
four cross-compiles, and nothing else in this repo puts a toolchain on
the runner, since check.yml does all of its work inside the
digest-pinned Dockerfile images. Without that step a tag either fails at
the before-hook or, worse, ships binaries built by whatever unpinned Go
the runner happens to carry -- the one unpinned thing in a release path
whose every other input is hash-pinned, in a repo whose policy admits no
exceptions and whose own script/release refuses a goreleaser that is not
the pinned build. actions/setup-go is pinned by commit sha like the
checkout above it, and reads its version from go.mod rather than
restating it.

An unobtainable version can no longer produce a binary at all. $(shell)
discards exit status, so a missing or broken script/version left VERSION
empty and the build went ahead and stamped nothing; the Makefile now
stops with an error instead. IsDevVersion("") became true as the second
line of defence, for a binary linked by something other than the
Makefile: nothing that knows its version reports no version, so an empty
version means the stamping failed, and a build that cannot be shown to
be a release is not one. This is the same defect class as the notice
that went silent above, one layer down.

Verified by running it: make release-snapshot produces the four
linux,darwin x amd64,arm64 archives plus checksums.txt, and the binary
from dist/ reports dev-<sha> with the development-build notice. Tag
handling was exercised in a throwaway repository; no tag was created
here, since that is the owner's call. Signing, SBOM, reproducible builds,
shell completions and a man page remain out of scope.

.gitea/workflows/release.yml

@@ -0,0 +1,60 @@
+name: release
+on:
+  push:
+    tags: ["v*"]
+jobs:
+  release:
+    runs-on: ubuntu-latest
+    steps:
+      # actions/checkout v4, 2024-09-16
+      - uses: actions/checkout@34e114876b0b11c390a56381ad16ebd13914f8d5
+        with:
+          # goreleaser needs the tags and the full history: the version
+          # it stamps comes from the tag, and the changelog comes from
+          # the commits since the previous one. A shallow checkout
+          # silently produces a mislabelled release.
+          fetch-depth: 0
+      # goreleaser is not a compiler: it shells out to `go` for the
+      # `before:` hook and for every one of the four cross-compiles.
+      # Nothing else in this repo puts a Go toolchain on the runner --
+      # check.yml runs script/cibuild, which does all of its work inside
+      # the digest-pinned Dockerfile images -- so without this step the
+      # release either fails at the before-hook or, worse, ships binaries
+      # built by whatever unpinned Go the runner happens to carry.
+      # REPO_POLICIES.md requires every external reference to be pinned,
+      # and script/release already refuses a goreleaser that is not the
+      # pinned build; the compiler that actually produces the artifacts
+      # is the last thing that should be exempt from that.
+      #
+      # go-version-file rather than a literal: go.mod's `go 1.26.1` is
+      # the single source of truth for the toolchain, the same way the
+      # Dockerfile FROM line is the single source of truth for the
+      # linter version that script/lint enforces. It is a three-component
+      # version, so setup-go resolves it exactly -- no silent drift onto
+      # a newer patch release.
+      #
+      # actions/setup-go v5.6.0, 2025-12-15. Pinned by commit sha, like
+      # the checkout above. v5.x is a node20 action, matching the node20
+      # actions/checkout v4 already in use here; the v6/v7 line requires
+      # a node24 runner, which this Gitea runner has never been asked
+      # for and cannot be assumed to provide.
+      - name: Install Go
+        uses: actions/setup-go@40f1582b2485089dde7abd97c1529aa768e1baff
+        with:
+          go-version-file: go.mod
+          # setup-go's module cache needs a runner-side cache backend.
+          # A release is cut rarely and a cold module download costs
+          # seconds; a release failing because a cache service is absent
+          # costs a re-tag. Off, deliberately.
+          cache: false
+      - name: Install goreleaser
+        run: script/install-goreleaser
+      - name: Release
+        run: script/release
+        env:
+          # RELEASE_TOKEN is a repository Actions secret: a Gitea access
+          # token with write access to this repository's releases (scope
+          # write:repository), owned by an account that can publish here.
+          # It is deliberately not the runner's automatic token, which is
+          # not guaranteed to carry that scope.
+          GITEA_TOKEN: ${{ secrets.RELEASE_TOKEN }}