feat: initial copr-publish composite action

Wraps copr-cli submit/watch/download-build with per-chroot log
dumping as collapsible ::group:: blocks. Moves the logic previously
living at .gitea/scripts/copr-build.sh in helexa/cortex into a
reusable action so every consumer gets live log visibility and
consistent failure diagnostics.

Inputs: project, srpm (glob OK), copr-config (secret).

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

README.md

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+# copr-publish
+
+Gitea composite action that submits a source RPM to [Fedora COPR](https://copr.fedorainfracloud.org/),
+watches the build, and dumps each chroot's `builder-live.log` into the
+CI output as collapsible groups.
+
+## Why use this
+
+`copr-cli build` by itself only prints status transitions
+(`pending` / `importing` / `running` / `succeeded`). When a build fails
+you have to click through to the COPR web UI to see the actual log.
+This action:
+
+- Submits with `--nowait` and captures the build ID.
+- Prints a clickable `https://copr.fedorainfracloud.org/coprs/build/...` link so you can follow live.
+- Watches the build to completion (blocks, propagates exit status).
+- On completion, fetches each chroot's `builder-live.log` via
+  `copr-cli download-build` and emits them as `::group::` blocks.
+- Fails CI if the build fails, but always dumps logs first.
+
+## Requirements
+
+The runner must already have:
+
+- `copr-cli` on `PATH` (provided by the `copr-cli` RPM on Fedora runners).
+- `grep -P` (PCRE, default on Fedora).
+
+## Inputs
+
+| Input         | Required | Description                                                                |
+| ------------- | -------- | -------------------------------------------------------------------------- |
+| `project`     | yes      | COPR project in the form `<owner>/<project>`, e.g. `helexa/cortex`.        |
+| `srpm`        | yes      | Path or glob to the source RPM(s) to submit, e.g. `*.src.rpm`.             |
+| `copr-config` | yes      | Contents of `~/.config/copr`. Fetch from <https://copr.fedorainfracloud.org/api/> and store as a repo or org secret. |
+
+## Usage
+
+```yaml
+jobs:
+  publish:
+    runs-on: fedora
+    steps:
+      - uses: actions/download-artifact@v3
+        with:
+          name: my-srpm
+
+      - name: Publish to COPR
+        uses: https://git.lair.cafe/actions/copr-publish@v1
+        with:
+          project: helexa/cortex
+          srpm: '*.src.rpm'
+          copr-config: ${{ secrets.COPR_CONFIG }}
+```
+
+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 (`@v1.0.3`) to freeze.
+
+## Obtaining `COPR_CONFIG`
+
+1. Log in to <https://copr.fedorainfracloud.org/>.
+2. Visit <https://copr.fedorainfracloud.org/api/>.
+3. Copy the entire `[copr-cli]` config block.
+4. Save as a Gitea secret named `COPR_CONFIG` in the consuming repo
+   (or at org level to share across all org repos).