ci: gitea actions for the suites, the image and the APK

Four workflows, none of which existed:

* `tests.yml` — backend, desktop, `:core` and the web app's typecheck+build, in
  parallel. `:core` needs no Android SDK at all, because settings.gradle.kts
  leaves `:app` out when there is none; `:app`'s Robolectric suite therefore
  lives in the APK workflow, where the SDK is installed anyway. Nothing needs a
  running backend — the suites feed on committed fixtures, which is the whole
  reason they were written that way.
* `lint.yml` — ruff, which the repo had been configured for and never run.
* `docker.yml` — builds the image, *starts* it against SQLite and waits for
  /api/health before pushing, then publishes `:latest` and `:<short-sha>` to
  git.timka.su. A tag nobody can run is worse than no tag.
* `android-release.yml` — the release APK on every push to master, signed from
  secrets, with `apksigner verify --print-certs` reporting which key was really
  used and failing if it was the debug one.

Three things the repo needed before any of that could work:

`versionCode` was pinned at 1, so every APK looked like the same version to the
phone and would not install over its predecessor. It now comes from the run
number, with `versionName` from a property, both via one `setting()` helper that
reads a Gradle property or an environment variable.

The release build fell back to the *debug* signing key whenever the keystore was
missing — silently. That is a trap: the APK installs, looks fine, and can never
be upgraded by a properly signed build. `KADENCE_REQUIRE_SIGNING=1` makes that
case fail the build instead, and the release job sets it whenever a keystore
secret is present.

The compose files built an image with no name, so there was nothing to pull.
`image:` now names the registry tag while `up --build` still builds locally.

Also: `android/ci/install-sdk.sh` (idempotent, cacheable, and the one place that
knows `platforms;android-37.0` is spelled with the minor version), the runner as
a compose service with its config and a setup checklist, six make targets, and a
README section. No runner is registered yet — `make ci-runner` is step two of
that checklist.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

android/ci/install-sdk.sh

@@ -0,0 +1,46 @@
+#!/usr/bin/env bash
+# Install just enough Android SDK to build this app, idempotently.
+#
+# Used by CI, and usable by hand on a fresh machine. Everything lands in
+# $ANDROID_HOME (default /opt/android-sdk), so pointing a cache or a volume at
+# that directory makes the whole thing a no-op on later runs.
+#
+# Two package names are worth knowing:
+#
+#   * `platforms;android-37.0` — Android's new minor-version scheme. Plain
+#     `android-37` does not exist and sdkmanager will not tell you why.
+#   * `build-tools;37.0.0` — needed for `apksigner`, which is how a release job
+#     proves what key it actually signed with.
+set -euo pipefail
+
+SDK_ROOT="${ANDROID_HOME:-/opt/android-sdk}"
+COMPILE_SDK="$(sed -n 's/^compileSdk = "\(.*\)"/\1/p' "$(dirname "$0")/../gradle/libs.versions.toml")"
+BUILD_TOOLS="${BUILD_TOOLS:-${COMPILE_SDK}.0.0}"
+CMDLINE_VERSION="13114758"  # cmdline-tools 17.0, the one that knows about minor platforms
+
+mkdir -p "$SDK_ROOT"
+
+if [ ! -x "$SDK_ROOT/cmdline-tools/latest/bin/sdkmanager" ]; then
+  echo "==> fetching cmdline-tools"
+  tmp="$(mktemp -d)"
+  curl -fsSL -o "$tmp/tools.zip" \
+    "https://dl.google.com/android/repository/commandlinetools-linux-${CMDLINE_VERSION}_latest.zip"
+  unzip -q "$tmp/tools.zip" -d "$tmp"
+  mkdir -p "$SDK_ROOT/cmdline-tools"
+  rm -rf "$SDK_ROOT/cmdline-tools/latest"
+  mv "$tmp/cmdline-tools" "$SDK_ROOT/cmdline-tools/latest"
+  rm -rf "$tmp"
+fi
+
+export PATH="$SDK_ROOT/cmdline-tools/latest/bin:$PATH"
+
+echo "==> licences"
+yes | sdkmanager --sdk_root="$SDK_ROOT" --licenses >/dev/null
+
+echo "==> platform-tools, platforms;android-${COMPILE_SDK}.0, build-tools;${BUILD_TOOLS}"
+sdkmanager --sdk_root="$SDK_ROOT" \
+  "platform-tools" \
+  "platforms;android-${COMPILE_SDK}.0" \
+  "build-tools;${BUILD_TOOLS}" >/dev/null
+
+echo "==> $SDK_ROOT is ready"