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.

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.

.goreleaser.yaml

@@ -2,6 +2,13 @@ version: 2
 
 project_name: vaultik
 
+# This repo lives on Gitea, not GitHub. Without this block goreleaser
+# talks to the GitHub API by default and a `goreleaser release` either
+# fails outright or publishes somewhere nobody is looking.
+gitea_urls:
+  api: https://git.eeqj.de/api/v1
+  download: https://git.eeqj.de
+
 before:
   hooks:
     - go mod tidy
@@ -37,8 +44,14 @@ checksum:
   name_template: "checksums.txt"
   algorithm: sha256
 
+# A snapshot is not a release and must not name itself like one. The
+# previous `{{ incpatch .Version }}-next` derived a plausible-looking
+# release number from the last tag -- and with no tags in the repo at
+# all, from goreleaser's fabricated v0.0.0. This produces the same
+# string script/version produces for an untagged build, so a snapshot
+# binary and a `make vaultik` binary of the same clean commit agree.
 snapshot:
-  version_template: "{{ incpatch .Version }}-next"
+  version_template: "dev-{{ slice .FullCommit 0 12 }}"
 
 changelog:
   sort: asc