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_runtime_clarity.py

@@ -35,7 +35,8 @@ CONFIG_SWITCHING_DISABLED = {
             "auth": {"type": "env", "name": "GITEA_TOKEN_AUTHOR"},
             "allowed_operations": ["gitea.read", "gitea.pr.create", "gitea.branch.push"],
             "forbidden_operations": ["gitea.pr.approve", "gitea.pr.merge"],
-            "execution_profile": "author-profile"
+            "execution_profile": "author-profile",
+        "allowed_repositories": ["Example-Org/Example-Repo"],
         },
         "reviewer-profile": {
             "enabled": True,
@@ -45,7 +46,8 @@ CONFIG_SWITCHING_DISABLED = {
             "auth": {"type": "env", "name": "GITEA_TOKEN_REVIEWER"},
             "allowed_operations": ["gitea.read", "gitea.pr.review", "gitea.pr.approve"],
             "forbidden_operations": ["gitea.pr.create", "gitea.branch.push", "gitea.pr.merge"],
-            "execution_profile": "reviewer-profile"
+            "execution_profile": "reviewer-profile",
+        "allowed_repositories": ["Example-Org/Example-Repo"],
         },
         "merger-profile": {
             "enabled": True,
@@ -55,7 +57,8 @@ CONFIG_SWITCHING_DISABLED = {
             "auth": {"type": "env", "name": "GITEA_TOKEN_MERGER"},
             "allowed_operations": ["gitea.read", "gitea.pr.merge"],
             "forbidden_operations": ["gitea.pr.create", "gitea.branch.push", "gitea.pr.approve"],
-            "execution_profile": "merger-profile"
+            "execution_profile": "merger-profile",
+        "allowed_repositories": ["Example-Org/Example-Repo"],
         }
     },
     "rules": {