ci: mutation testing is local only (D-59); the weekly run keeps proofs, oracle and fuzz

The owner, 2026-10-29: mutation testing is for local runs, not CI. The
weekly workflow's mutation shards (core, store, import, config, MCP) are
removed; they failed every week on the survivors and timeouts D-33
deferred to P12, and their red hid the run's real findings (a
fuzz_store_replay crash and a fuzz_settings_replay build break, both
being fixed). just mutants-* stays for the desktop; P12 runs the pass
whole. Recorded as D-59; the docs that said the shards keep running are
corrected.

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

README.md

@@ -51,9 +51,9 @@ oracles, never ship what they haven't demonstrated.
   pass found three engine bugs that every test, fuzzer, and mutant had
   missed: negative amounts accepted, and two crashes on oversized
   amounts. It also caught a soundness bug in the model checker itself.
-- Mutation testing via cargo-mutants (paused for development until the
-  P12 max-testing pass, D-33; CI's weekly shards still run); fuzzing via
-  cargo-fuzz (11.5M+ executions, zero crashes).
+- Mutation testing via cargo-mutants, a local run (paused for development
+  until the P12 max-testing pass, D-33; not a CI job, D-59); fuzzing via
+  cargo-fuzz (11.5M+ executions, zero crashes), weekly in CI.
 - GnuCash is *a* behavioral cross-check, never the authority and never
   a code source (clean room, MIT OR Apache-2.0). Accounting principles,
   proved, are the spec. Where any other program disagrees, we work out