build: add Docker-only Makefile, SDK setup and product manifest

- Makefile: every target runs in a container as your UID/GID, with no
  capabilities, a read-only root filesystem, only the project folder
  mounted and no network except for image builds and `make sdk`.
  Serial even under `make -j`. `make nuke` removes containers, images,
  the dedicated buildx builder and .cache/ after confirmation.
- sdk-setup.sh: agreement acceptance pinned to the hash you read,
  password login (never stored), SDK 9.2.0 and device download, and
  the login token deleted afterwards.
- gen-key.sh: RSA-4096 developer key into .cache/keys, never
  overwritten, with backup instructions.
- manifest.xml: watch-app, minApiLevel 5.0.0, no permissions, and the
  72 watches with API 5.0+ and at least 512 KB for apps.
- .gitignore, lint configs and CHANGELOG.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

1 files changed, 26 insertions, 0 deletions

diff --git a/.gitignore b/.gitignore
new file mode 100644
index 0000000..8da1c0d
--- /dev/null
+++ b/.gitignore
@@ -0,0 +1,26 @@
+# Local tool state: Garmin SDK, device files, SDK-manager login token and the
+# developer key. Never commit any of it (Garmin's licence, and the key signs
+# every release).
+/.cache/
+
+# Build outputs.
+/build/
+/bin/
+
+# Signing keys and signed artifacts, wherever they end up.
+*.der
+*.pem
+*.prg
+*.iq
+*.prg.debug.xml
+
+# Python tooling caches.
+__pycache__/
+*.py[cod]
+.pytest_cache/
+.mypy_cache/
+.ruff_cache/
+.hypothesis/
+
+# Node modules are installed only inside the docs image.
+node_modules/