chore: hygiene pass — ruff clean, docs storage-model truth, replay /me, failSession log

Audit findings 6.1-6.4 + the audit's remediation plan itself
(docs/superpowers/plans/2026-07-20-full-audit-remediation-plan.md).

- ruff: 34 → 0 (unused imports/f-strings auto-fixed; E702 semicolon lines
  split in test files; one unused local dropped). Suite still 819 green.
- CLAUDE.md + PROJECT_STATE.md no longer claim "no database / settings in
  settings.json": the harness selects filesystem OR PostgreSQL session
  storage (repository.py, server mode), and settings flow through harness
  preferences with the JSON file as fallback only.
- tools/replay: stub /me (SPA boot was parsing the SPA's own HTML as JSON)
  and /runtime/prewarm.
- failSession best-effort persistence now logs its failure server-side
  instead of vanishing.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

harness/tests/test_formula.py

@@ -6,9 +6,7 @@ surfaces a candidate formula, the reviewer approves or rejects it (recorded via
 concept_formula_approved / concept_formula_rejected), and approved formulas are
 part of the schema-linking artifact. The store is frontmatter-YAML + SQL body.
 """
-from pathlib import Path
 
-import pytest
 
 from tht.evidence.formula_store import ConceptFormula, retrieve_formula, save_formula