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/service/auth/auth_test.go

@@ -121,7 +121,7 @@ func getSessionCookie(t *testing.T, svc *auth.Service) *http.Cookie {
 	require.NoError(t, err)
 
 	recorder := httptest.NewRecorder()
-	request := httptest.NewRequest(http.MethodGet, "/", nil)
+	request := httptest.NewRequestWithContext(t.Context(), http.MethodGet, "/", nil)
 
 	err = svc.CreateSession(recorder, request, user)
 	require.NoError(t, err)
@@ -144,7 +144,11 @@ func TestSessionCookieSecureFlag(testingT *testing.T) {
 		svc := setupAuthService(t, false)
 		cookie := getSessionCookie(t, svc)
 		require.NotNil(t, cookie, "session cookie should exist")
-		assert.True(t, cookie.Secure, "session cookie should have Secure flag in production mode")
+		assert.True(
+			t,
+			cookie.Secure,
+			"session cookie should have Secure flag in production mode",
+		)
 	})
 }
 
@@ -324,7 +328,12 @@ func TestCreateUserRaceCondition(testingT *testing.T) {
 		}
 
 		assert.Equal(t, 1, successes, "exactly one goroutine should succeed")
-		assert.Equal(t, goroutines-1, failures, "all other goroutines should fail with ErrUserExists")
+		assert.Equal(
+			t,
+			goroutines-1,
+			failures,
+			"all other goroutines should fail with ErrUserExists",
+		)
 	})
 }
 
@@ -380,7 +389,9 @@ func TestDestroySessionMaxAge(testingT *testing.T) {
 		defer cleanup()
 
 		recorder := httptest.NewRecorder()
-		request := httptest.NewRequest(http.MethodGet, "/", nil)
+		request := httptest.NewRequestWithContext(
+			t.Context(), http.MethodGet, "/", nil,
+		)
 
 		err := svc.DestroySession(recorder, request)
 		require.NoError(t, err)