ci: weekly store mutation run and replay fuzzing

`just mutants-store` (64 random cases per mutant, temp books on a RAM
disk in CI) runs beside the core's weekly; fuzz_store_replay joins the
weekly fuzz matrix. docs/testing.md lists the spec-blind store suite,
the refusal property's converse law, and the replay fuzz oracles.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01GWVo7x3UHw5kwCUaWxiejX

.github/workflows/scheduled.yml

@@ -22,7 +22,7 @@ jobs:
     strategy:
       fail-fast: false
       matrix:
-        target: [fuzz_journal_line, fuzz_entry_validate, fuzz_op_sequence, fuzz_core_serde, fuzz_store_open]
+        target: [fuzz_journal_line, fuzz_entry_validate, fuzz_op_sequence, fuzz_core_serde, fuzz_store_open, fuzz_store_replay]
     steps:
       - uses: actions/checkout@v4
       - uses: jdx/mise-action@v2
@@ -33,8 +33,11 @@ jobs:
       - uses: actions/checkout@v4
       - uses: jdx/mise-action@v2
       - run: just mutants
+      - run: TMPDIR=/dev/shm just mutants-store
       - if: always()
         uses: actions/upload-artifact@v4
         with:
           name: mutants
-          path: mutants.out
+          path: |
+            mutants.out
+            mutants-store/mutants.out