CI/CD hardening: lint, secret scan, coverage gate, auto CVE-fix PRs, GHCR + GitHub mirror publishing (#32)

- release changelog: commits rendered as description (link), divider lines dropped
- gitleaks secret scan and hadolint on every push/PR
- ruff lint/format gate (Python repos) with a pytest --cov-fail-under gate
- scheduled CRITICAL Trivy failures attempt an apk upgrade rebuild and open a follow-up PR if it clears the finding, instead of just failing red
- images also published to ghcr.io/djeex/<repo>
- a matching GitHub Release is created on the GitHub mirror, with a notice pointing back to this repo as the source of truth

ruff.toml

@@ -0,0 +1,13 @@
+line-length = 100
+
+[lint]
+select = ["E", "F", "I", "UP", "B"]
+# E501: handled by the formatter. B905: zip() without strict= in env_config.py —
+# app-logic change, left for the user to decide (see feedback-no-app-logic-changes).
+ignore = ["E501", "B905"]
+
+[lint.isort]
+# Pinned explicitly: auto-detection of first-party modules differs between the
+# host (app/ subdir + .git present) and the Docker lint stage (flattened to /app,
+# no .git) — without this, import-sort results silently diverge between the two.
+known-first-party = ["env_config", "gpu_checker", "notifier", "main"]