feat: initial rpm-changelog composite action

Generates an rpm %changelog entry from git history and prepends it
to the target spec file. Runs in release CI so every tag push gets
a fresh dated entry covering the commits since the previous matching
tag. Avoids stale dates, forgotten bumps, and bogus-weekday warnings.

Inputs: spec path, version, optional release suffix, author,
tag-pattern, exclude-patterns. The last two make the defaults (v*
tags, filter bump-version chores and merges) tweakable for projects
with different conventions.

Migrated from inline logic in helexa/cortex so any project can
adopt the same pattern with a single uses: reference.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

README.md

@@ -0,0 +1,103 @@
+# rpm-changelog
+
+Gitea composite action that generates an rpm `%changelog` entry from
+git history and prepends it to a spec file. Designed to run during
+release CI so the changelog never drifts out of sync with the code.
+
+## Why use this
+
+Hand-maintained rpm `%changelog` sections drift. The day-of-week gets
+stale, the version lags behind tags, and the description stops
+matching what actually changed. This action:
+
+- Finds the previous release tag (default pattern `v*`).
+- Collects commits between that tag and `HEAD` via `git log`.
+- Filters out noise (bump-version bot commits, merge commits — both
+  configurable).
+- Writes a fresh `%changelog` entry with today's date, the release
+  author, and the new version.
+- Prepends it to the spec file's existing `%changelog` section.
+
+Because the date is generated at build time, `rpmbuild` will never
+warn about bogus weekdays and the entry always reflects what changed
+since the last release.
+
+## Requirements
+
+The consumer workflow must check out the repo with full git history:
+
+```yaml
+- uses: actions/checkout@v4
+  with:
+    fetch-depth: 0
+```
+
+Without this, `git describe` can't see prior tags and the entry will
+default to "No user-visible changes" on every release.
+
+## Inputs
+
+| Input              | Required | Default                                       | Description                                                                 |
+| ------------------ | -------- | --------------------------------------------- | --------------------------------------------------------------------------- |
+| `spec`             | yes      | —                                             | Path to the rpm spec file to update.                                        |
+| `version`          | yes      | —                                             | Version string for the new entry (without release suffix), e.g. `0.1.10`.   |
+| `release`          | no       | `1`                                           | Release suffix to append after the version.                                 |
+| `author`           | no       | `Gitea Actions <actions@git.lair.cafe>`       | Name and email for the entry.                                               |
+| `tag-pattern`      | no       | `v*`                                          | Glob pattern for release tags, used to locate the previous release.         |
+| `exclude-patterns` | no       | (see below)                                   | Newline-separated `grep -E` patterns to drop from the generated log.        |
+
+Default `exclude-patterns`:
+
+```
+^- chore: bump version
+^- Merge
+```
+
+## Usage
+
+```yaml
+jobs:
+  srpm:
+    runs-on: fedora
+    if: startsWith(github.ref, 'refs/tags/v')
+    steps:
+      - uses: actions/checkout@v4
+        with:
+          fetch-depth: 0
+
+      - name: Determine version
+        id: version
+        run: echo "VERSION=${GITHUB_REF#refs/tags/v}" >> "$GITHUB_OUTPUT"
+
+      - name: Stamp version in spec
+        run: sed -i "s/^Version:.*/Version:        ${{ steps.version.outputs.VERSION }}/" mypackage.spec
+
+      - name: Update changelog
+        uses: https://git.lair.cafe/actions/rpm-changelog@v1
+        with:
+          spec: mypackage.spec
+          version: ${{ steps.version.outputs.VERSION }}
+
+      - name: Build SRPM
+        run: rpmbuild -bs mypackage.spec --define "_sourcedir $(pwd)"
+```
+
+Note the fully-qualified URL in `uses:` — the Gitea instance's
+`DEFAULT_ACTIONS_URL` points at github.com, so internal actions must
+be referenced by absolute URL.
+
+## Versioning
+
+Pin to a major version tag (`@v1`) for automatic patch/minor updates.
+Pin to an exact tag (`@v1.0.2`) to freeze.
+
+## Behaviour notes
+
+- If no previous tag matching `tag-pattern` exists (first release),
+  the entry body becomes `- No user-visible changes`.
+- If the filter removes every commit (e.g. release contained only
+  bump-version chores), body is `- No user-visible changes`.
+- The spec file must already contain a `%changelog` line — the
+  action will error out rather than mangle an unmarked file.
+- The date uses UTC (`date -u`) so runners in different timezones
+  produce deterministic output.