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_role_namespace_gate.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 reviewer/author namespace mismatch walls (#209)."""
 import json
 import os
@@ -36,6 +40,7 @@ CONFIG = {
                 "gitea.pr.approve", "gitea.pr.merge", "gitea.pr.review",
             ],
             "execution_profile": "prgs-author",
+        "allowed_repositories": ["Scaled-Tech-Consulting/Gitea-Tools"],
         },
         "prgs-reviewer": {
             "enabled": True,
@@ -51,6 +56,7 @@ CONFIG = {
                 "gitea.pr.create", "gitea.branch.push", "gitea.issue.create",
             ],
             "execution_profile": "prgs-reviewer",
+        "allowed_repositories": ["Scaled-Tech-Consulting/Gitea-Tools"],
         },
         "prgs-reviewer-issue-writer": {
             "enabled": True,
@@ -63,12 +69,13 @@ CONFIG = {
             ],
             "forbidden_operations": ["gitea.pr.create"],
             "execution_profile": "prgs-reviewer-issue-writer",
+        "allowed_repositories": ["Scaled-Tech-Consulting/Gitea-Tools"],
         },
     },
     "rules": {"allow_runtime_switching": False},
 }
 
-ISSUE_WRITE_ENV = {"GITEA_ALLOWED_OPERATIONS": "gitea.issue.create"}
+ISSUE_WRITE_ENV = {}  # config-backed; operations come from profile allowlist (#714)
 
 
 class NamespaceGateBase(unittest.TestCase):
@@ -199,7 +206,7 @@ class TestMutationAuditFields(NamespaceGateBase):
     def test_successful_create_issue_audit_includes_namespace_fields(
         self, _auth, mock_api, _get_all, _role
     ):
-        env = {**self._env("prgs-author", audit=True), **ISSUE_WRITE_ENV}
+        env = self._env("prgs-author", audit=True)
         with patch.dict(os.environ, env, clear=True):
             mcp_server.gitea_create_issue(title="audited", remote="prgs")
         with open(self.audit_path, encoding="utf-8") as fh: