ci: keep a fuzz crash's input as an artifact

The 2026-10-26 weekly run found a fuzz_store_replay crash (the writer
and the viewer disagreeing on a journal with an unknown convention kind)
and uploaded nothing, so the input is being hunted again locally. A
failing fuzz job now uploads fuzz/artifacts.

Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01HS8WZziDnyxunC23MUxrLp

.github/workflows/scheduled.yml

@@ -38,3 +38,11 @@ jobs:
       - uses: actions/checkout@v4
       - uses: jdx/mise-action@v2
       - run: just fuzz ${{ matrix.target }} 600
+      # A crash's input is the finding: keep it (the 2026-10-26 run found one
+      # in fuzz_store_replay and kept nothing, so it had to be hunted again).
+      - if: failure()
+        uses: actions/upload-artifact@v4
+        with:
+          name: fuzz-${{ matrix.target }}-artifacts
+          path: fuzz/artifacts
+          if-no-files-found: ignore