feat: tag and publish a Gitea release on every push to master

A plugin installed as a bare git+https URL is pinned to a commit, so with no
tags there is nothing for `dsh plugin update` to move to. The workflow reads
the commit subjects since the last tag, bumps package.json, prepends
CHANGELOG.md, tags vX.Y.Z, and publishes the Gitea release with those subjects
as the body. The decision logic lives in .gitea/scripts/release.sh so it runs
and is tested without a runner (`npm run test:release`).

AGENTS.md

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+# Working in this repository
+
+`master` releases itself. Every push runs `.gitea/workflows/release.yml`, which
+reads the commit subjects since the last tag, bumps `package.json`, prepends
+`CHANGELOG.md`, tags `vX.Y.Z`, and publishes the Gitea release with those
+subjects as the body.
+
+## Commit subjects are release input
+
+The subject is both the version decision and the sentence a user reads in the
+release notes. Write it for that reader:
+
+- `feat: …` — the change adds a capability. Minor bump: `0.1.0` → `0.2.0`.
+- `feat!: …` or `fix(x)!: …` — the change breaks an existing install. Major
+  bump: `0.1.0` → `1.0.0`, and the note lands under **Breaking**. `[major]`
+  anywhere in the subject does the same when a `!` will not fit.
+- `fix: …`, `docs: …`, or a plain sentence — everything else. Patch bump:
+  `0.1.0` → `0.1.1`.
+- `[skip release]` — this push publishes nothing.
+
+`feat` has to be a word, so `Fix the feature flag leak` is a patch. Only the
+subject line is read; the body is not.
+
+## The release job owns the version and the changelog
+
+`package.json`'s `version` and `CHANGELOG.md` are the job's to write, derived
+from the commits. Pushing to `master` is the whole trigger — the tag and the
+release come with it.
+
+## Checking before pushing
+
+```sh
+npm run release:plan     # would this HEAD release? (yes/no)
+npm run release:notes    # the exact notes it would publish
+npm run test:release     # the checks behind the bump and the notes
+```
+
+The rules in full — the marker table, first-release behaviour, how prose commits
+are handled — are in the README under *Releases*.