ci: Upload fuzz crash artifacts on failure

When a fuzzer crashes, the crash-reproducing input and logs are now
saved as GitHub Actions artifacts, making it possible to download
and reproduce failures locally without re-running long fuzz sessions.

Assisted-by: OpenCode (Claude Opus)

Author: cgwalters

.github/workflows/ci.yaml

@@ -98,3 +98,11 @@ jobs:
         run: just generate-corpus
       - name: Fuzz all targets (2 minutes each)
         run: just fuzz-all
+      - name: Upload fuzz artifacts
+        if: failure()
+        uses: actions/upload-artifact@v4
+        with:
+          name: fuzz-artifacts
+          path: |
+            fuzz/artifacts/
+            target/fuzz-logs/

.github/workflows/fuzz-extended.yaml

@@ -34,3 +34,11 @@ jobs:
         run: just generate-corpus
       - name: Fuzz all targets (15 minutes each)
         run: just fuzz-all 900
+      - name: Upload fuzz artifacts
+        if: failure()
+        uses: actions/upload-artifact@v4
+        with:
+          name: fuzz-artifacts
+          path: |
+            fuzz/artifacts/
+            target/fuzz-logs/