Update golangci-lint to v2.12.2 with canonical config

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.

internal/middleware/middleware.go

@@ -370,8 +370,9 @@ func (m *Middleware) LoginRateLimit() func(http.Handler) http.Handler {
 	}
 }
 
-// APISessionAuth returns middleware that requires session authentication for API routes.
-// Unlike SessionAuth, it returns JSON 401 responses instead of redirecting to /login.
+// APISessionAuth returns middleware that requires session authentication
+// for API routes. Unlike SessionAuth, it returns JSON 401 responses instead
+// of redirecting to /login.
 func (m *Middleware) APISessionAuth() func(http.Handler) http.Handler {
 	return func(next http.Handler) http.Handler {
 		return http.HandlerFunc(func(