docs: sync mumei-side live generated theorem path count to thirteen

[AkiraTamai]

Summary

docs-sync only. docs/CROSS_PROJECT_ROADMAP.md §SI-6 already lists 13 live generated Lean bridge paths (through predicate_guard_collapse), but three other places still carried stale counts:

• docs/STDLIB.md: "eight live generated theorem paths" + 8-item list → thirteen, adding rtgs_transfer_conservation, ff_mul_commutative, ff_mul_associative, ff_mul_add_distributive, predicate_guard_collapse.
• docs/ROADMAP.md: "(ten in total: …)" → thirteen with the same list.
• docs/CROSS_PROJECT_ROADMAP.md V1 summary table/prose (10 live generated theorem paths → 13), noting that paths 12/13 have no bridge lemma template and are adopted by the deterministic 16-candidate tactic search (mumei_ff_mod / tauto), so bridge_lemma_hash is unchanged.

Source of truth is the mumei-lean implementation (tests/test_lean_bridge_e2e.py + the 13 live *.proof-cert.json fixtures); the matching mumei-lean docs sync is mumei-lang/mumei-lean#109. No vocabulary, verdict, or audit-key change: harness_contract, intent_fidelity, artifact_paths, budget_policy_fingerprint, lean_verified and the 8 fixed audit keys are untouched.

Regression commands

# mumei
python3 scripts/check_contract_vocabulary.py           # passed
python3 scripts/generate_stdlib_metrics.py --mumei-bin target/debug/mumei
#   → 59 modules (59 OK / 0 FAIL / 0 SKIP), 344 atoms (344 proven · 0 trusted), health 1.000
#     i.e. docs/STDLIB_METRICS.md already matches the implementation; no regeneration needed here.

# mumei-agent
uv run pytest tests/test_contract_vocabulary.py -q     # 7 passed

# mumei-lean
PYTHONPATH=scripts MUMEI_LEAN_SKIP_LIVE=1 python -m pytest -q   # 306 passed, 11 skipped

Link to Devin session: https://app.devin.ai/sessions/adfa18cdf78948c09b218b54aa5a83b0
Requested by: @AkiraTamai

[devin-ai-integration]

🤖 Devin AI Engineer

I'll be helping with this pull request! Here's what you should know:

✅ I will automatically:

• Address comments on this PR. Add '(aside)' to your comment to have me ignore it.
• Look at CI failures and help fix them

Note: I can only respond to comments from users who have write access to this repository.

⚙️ Control Options:

• Disable automatic comment, CI, and merge conflict monitoring

[devin-ai-integration]

✅ Devin Review: No Issues Found

Devin Review analyzed this PR and found no bugs or issues to report.