v0.1.1: run tests in CI, add REUSE compliance and CONTRIBUTING

- Add .github/workflows/test.yml, using flatpak-builder's run-tests
  option so PRs and pushes exercise ctest inside the same KDE SDK
  sandbox as release builds.
- Add REUSE.toml covering files that can't carry an inline SPDX header
  (.desktop, keys/*.asc).
- Add CONTRIBUTING.md documenting build/test/release steps.

CONTRIBUTING.md

@@ -0,0 +1,50 @@
+# Contributing to Kareer
+
+## Build
+
+Kareer is a KDE/Kirigami application (C++20 + QML) built with CMake and
+Extra CMake Modules. See the README for the full list of system packages
+to install, then:
+
+```sh
+cmake -B build -G Ninja
+cmake --build build
+./build/bin/kareer
+```
+
+Every GUI action is also available from the `kareer` CLI
+(`add|list|show|update|stage|delete|stats|stages`) — run `./build/bin/kareer
+--help` to see the subcommands.
+
+## Test
+
+```sh
+ctest --test-dir build --output-on-failure
+```
+
+Tests live in `autotests/` and link the core logic directly out of `src/`
+(see `autotests/CMakeLists.txt`). CI runs the same suite on every pull
+request via `.github/workflows/test.yml`, using `flatpak-builder`'s
+`run-tests` option so the run happens inside the same KDE SDK sandbox as
+release builds.
+
+## Conventions
+
+- Every source file starts with `SPDX-License-Identifier: GPL-3.0-or-later`
+  (in whatever comment syntax fits the file type). Files that can't carry
+  an inline header — `.desktop`, `keys/*.asc` — are covered instead by
+  `REUSE.toml`.
+- `src/` is intentionally flat: one class per concern, no `models/`,
+  `controllers/`, or `viewmodels/` subfolders.
+- C++ backend classes are exposed to QML via `QML_ELEMENT`; QML views are
+  meant to stay thin renderers over that state, not hold logic themselves.
+- `JobsDatabase` is the only class that touches the SQLite database
+  directly — route all persistence changes through it.
+
+## Releasing
+
+`.github/workflows/build.yml` builds, signs, and publishes a Flatpak
+bundle whenever a `v*` tag is pushed. To cut a release: bump
+`project(... VERSION ...)` in `CMakeLists.txt`, add a matching `<release>`
+entry to the metainfo file, update the manifest's pinned `tag:`, then tag
+and push.