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_lock_issue_mcp_registration.py

@@ -1,7 +1,11 @@
-"""Regression tests for gitea_lock_issue MCP tool registration (#521)."""
-
 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 tempfile
 import unittest
@@ -13,22 +17,20 @@ from mcp_server import gitea_create_pr, gitea_lock_issue
 
 FAKE_AUTH = "Basic dGVzdDp0ZXN0"
 
-ISSUE_WRITE_ENV = {
-    "GITEA_ALLOWED_OPERATIONS": (
-        "gitea.issue.create,gitea.issue.close,gitea.issue.comment"
-    ),
-}
+ISSUE_WRITE_ENV = shared_mutation_env(
+    "test-author-prgs",
+)
 
-CREATE_PR_ENV = {
-    "GITEA_PROFILE_NAME": "author-test",
-    "GITEA_ALLOWED_OPERATIONS": (
+CREATE_PR_ENV = shared_mutation_env(
+    "test-author-prgs",
+    GITEA_ALLOWED_OPERATIONS=(
         "gitea.read,gitea.pr.create,gitea.branch.push,"
         "gitea.issue.create,gitea.issue.close,gitea.issue.comment"
     ),
-    "GITEA_FORBIDDEN_OPERATIONS": (
+    GITEA_FORBIDDEN_OPERATIONS=(
         "gitea.pr.approve,gitea.pr.merge,gitea.pr.review"
     ),
-}
+)
 
 
 def _clean_master_git_state_for_lock():