fix(session): require config-backed mutation authority and workspace-bound targets (#714)

Close the #714 remediation gap left at 943d402 where env-only mutation
profiles, REMOTES Timesheet defaults treated as explicit caller input, and
machine-dependent Git remotes produced false greens.

- Fail closed when mutations lack a config-backed profile with non-empty
  allowed_repositories; env ops cannot invent mutation authority.
- Preserve omitted-vs-explicit org/repo provenance through the mutation
  gate; omitted targets bind to the verified workspace repository.
- Prefer workspace-aligned Git remotes over historical Timesheet defaults
  in MCP _resolve and CLI resolve_remote.
- Centralize deterministic config-backed mutation fixtures; migrate
  mutation tests off env-only authority without weakening security
  assertions.

Full suite: 2744 passed, 6 skipped.

tests/test_stale_review_decision_lock_cleanup.py

@@ -1,15 +1,11 @@
-"""Stale #332 review-decision lock cleanup (#594).
-
-Proves:
-  a. active terminal locks still block unrelated terminal reviews
-  b. merged/closed PR locks can be cleared canonically
-  c. cleanup cannot bypass review gates on open PRs
-  d. after moot cleanup, mark_ready for a different PR can proceed
-     (PR #592-style after PR #586-style stale approve)
-"""
-
 from __future__ import annotations
 
+
+import sys as _sys
+from pathlib import Path as _Path
+_sys.path.insert(0, str(_Path(__file__).resolve().parent))
+from mutation_profile_fixture import shared_mutation_env  # noqa: E402
+
 import os
 import unittest
 from unittest.mock import patch