fix(dockerfile): use case-insensitive scratch comparison

Change "scratch".equals(image) to "scratch".equalsIgnoreCase(image)
so FROM SCRATCH, FROM Scratch, and other case variants are properly
skipped during Dockerfile parsing, matching the case-insensitive
handling of the FROM keyword itself.

Fixes: TC-5098
Assisted-by: Claude Code

Author: a-oren

src/main/java/io/github/guacsec/trustifyda/providers/DockerfileProvider.java

@@ -137,7 +137,7 @@ static List<String> parseAllFromImages(Path dockerfile) throws IOException {
               continue;
             }
           }
-          if ("scratch".equals(image)) {
+          if ("scratch".equalsIgnoreCase(image)) {
             LOG.info(String.format("Skipping FROM scratch in %s", dockerfile));
             continue;
           }

src/test/java/io/github/guacsec/trustifyda/providers/Dockerfile_Provider_Test.java

@@ -217,6 +217,17 @@ void skips_scratch_and_returns_remaining_images() throws IOException {
       assertThat(images).doesNotContain("scratch");
     }
 
+    /** Verifies that FROM SCRATCH (uppercase) is skipped case-insensitively. */
+    @Test
+    void skips_scratch_case_insensitively() throws IOException {
+      var dockerfile = TEST_MANIFESTS.resolve("scratch_uppercase/Dockerfile");
+
+      List<String> images = DockerfileProvider.parseAllFromImages(dockerfile);
+
+      assertThat(images).hasSize(1).containsExactly("node:18");
+      assertThat(images).doesNotContain("SCRATCH");
+    }
+
     /** Verifies that a Dockerfile with no analyzable FROM instructions throws IOException. */
     @Test
     void throws_when_no_analyzable_from_instruction() {

src/test/resources/tst_manifests/dockerfile/scratch_uppercase/Dockerfile

@@ -0,0 +1,8 @@
+FROM node:18 AS builder
+
+WORKDIR /app
+RUN npm ci
+
+FROM SCRATCH
+
+COPY --from=builder /app/dist /