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_agent_temp_artifacts.py

@@ -1,3 +1,7 @@
+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
 """Tests for agent temp artifact detection and preflight warnings (#261)."""
 import json
 import os
@@ -65,11 +69,9 @@ class TestPreflightWarnings(unittest.TestCase):
 # Issue-write tools are profile-gated (#69); gitea_lock_issue requires
 # gitea.issue.comment (see task_capability_map), so the gate must be
 # seeded exactly like tests/test_mcp_server.py::TestIssueLocking (#359).
-ISSUE_WRITE_ENV = {
-    "GITEA_ALLOWED_OPERATIONS": (
-        "gitea.issue.create,gitea.issue.close,gitea.issue.comment"
-    ),
-}
+ISSUE_WRITE_ENV = shared_mutation_env(
+    "test-author-prgs",
+)
 
 
 class TestIssueLockArtifactWarning(unittest.TestCase):