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

docs/oracle.md

@@ -53,7 +53,7 @@ case: partial first/final months in different-length calendar months don't
 complement, so the lifetime total drifted by cents (fixed with the
 final-month true-up in `depreciation_schedule`).
 
-**Layer 3 — Mutation testing (paused for development until P12, D-33, 2026-10-20; CI's weekly shards still run).** `cargo mutants -p ledger-core`
+**Layer 3 — Mutation testing (a local run, never a CI job, D-59; paused for development until P12, D-33).** `cargo mutants -p ledger-core`
 (228 mutants as of 2026-10-10: 159 caught, 28 unviable, 2 timeouts from
 induced infinite loops, 39 missed). Every *missed* mutant is triaged:
 real gaps get new tests (this pass added parent-account validation,