Bump golangci-lint from v2.10.1 to v2.12.2 in the Dockerfile lint
stage (tag+digest pin) and script/bootstrap release-archive pins
(linux amd64/arm64 sha256s). Replace .golangci.yml with the canonical
v2-layout config so linter settings (lll 88, funlen 80/50, cyclop 15,
dupl 100) actually apply.
Fix all findings surfaced by the new linter and config:
- noctx: use httptest.NewRequestWithContext in all tests
- gosec G710/G703: route app redirects through a path-escaping
redirectToApp helper; annotate internal log path usage
- goconst: introduce shared constants for template/JSON keys and
repeated test literals
- lll: wrap lines to the 88-column limit
- dupl: extract shared helpers (generic findAllByAppID in models,
deleteAppResource in handlers, parsePush in webhook payloads,
table-driven/helper-based test dedup)
- nolintlint: drop nolint directives made obsolete by the new limits
Record the change in TODO.md; make check is green.
