ci(release): auto-generate release notes via git-cliff

Replace the image-only tag pipeline with a full release workflow that also
publishes a Gitea Release whose body is the annotated tag's message,
generated from Conventional Commits by git-cliff. No hand-written release
notes are required.

- cliff.toml: group commits (Features, Bug Fixes, Refactor, Documentation,
  Tests, Miscellaneous Tasks) with scopes and short-SHA links; emit only the
  current tag's section rather than the full history.
- .gitea/workflows/release.yml: tag-driven. Reads the release body from the
  annotated tag (git tag -l --format), so the tag message and release body are
  a single source of truth. Idempotent create/PATCH; prints the Gitea API
  error body on failure so a 403 names the missing token scope instead of
  failing silently. Adds a workflow_dispatch tag input so manual re-runs
  target the right tag instead of the default branch.
- Makefile: release VERSION=vX.Y.Z generates notes via git cliff --latest
  against a throwaway tag, then creates an annotated tag with
  --cleanup=verbatim so the markdown group headers are preserved (git's
  default cleanup strips lines starting with "#").
- release: project-attached wrapper accepting a positional version arg
  (./release 0.3.0 or ./release v0.3.0) and auto-prefixing v, for ergonomic
  one-command releases.

cliff.toml

@@ -0,0 +1,37 @@
+# git-cliff configuration — generates the body of each Gitea Release from
+# Conventional Commits accumulated since the previous tag. Invoked in CI by
+# orhun/git-cliff-action with --latest so only the current tag's section is
+# emitted (no full history, no header — the Gitea Release title is the tag).
+# Docs: https://git-cliff.org/docs/configuration
+
+[changelog]
+header = ""
+body = """
+{% for group, commits in commits | group_by(attribute="group") %}\
+### {{ group | upper_first }}
+{% for commit in commits %}\
+- {% if commit.scope %}*({{ commit.scope }})* {% endif %}{{ commit.message | upper_first }} ({{ commit.id | truncate(length=7, end="") }})
+{% endfor %}\
+{% endfor %}\
+"""
+trim = true
+footer = ""
+
+[git]
+conventional_commits = true
+filter_unconventional = false
+require_conventional = false
+split_commits = false
+commit_parsers = [
+  { message = "^feat", group = "Features" },
+  { message = "^fix", group = "Bug Fixes" },
+  { message = "^perf", group = "Performance" },
+  { message = "^refactor", group = "Refactor" },
+  { message = "^docs", group = "Documentation" },
+  { message = "^test", group = "Tests" },
+  { message = "^chore|^ci", group = "Miscellaneous Tasks" },
+  { message = ".*", group = "Other" },
+]
+filter_commits = false
+tag_pattern = "v[0-9].*"
+sort_commits = "oldest"