fix(cli): fix project context show test mock for tier service

Add ContextTierService mock to step_m5_invoke_project_context_show
so the CLI command can call _get_context_tier_service() without
failing. Also patch _load_policy_json to prevent JSON decode errors
from MagicMock session objects. Update CHANGELOG.md and CONTRIBUTORS.md.

ISSUES CLOSED: #6323

robot/helper_project_context_cli.py

@@ -359,9 +359,7 @@ def test_context_show_acms_config() -> None:
 
     envelope = json.loads(output.strip())
     if envelope.get("command") != "project context show":
-        raise AssertionError(
-            f"Unexpected command value: {envelope.get('command')}"
-        )
+        raise AssertionError(f"Unexpected command value: {envelope.get('command')}")
 
     payload = envelope.get("data")
     if not isinstance(payload, dict):
@@ -369,9 +367,7 @@ def test_context_show_acms_config() -> None:
 
     context_policy = payload.get("context_policy")
     if not isinstance(context_policy, dict):
-        raise AssertionError(
-            f"Missing context_policy in payload: {payload.keys()}"
-        )
+        raise AssertionError(f"Missing context_policy in payload: {payload.keys()}")
     if context_policy.get("project") != "local/ctx-robot":
         raise AssertionError(
             f"context_policy project mismatch: {context_policy.get('project')}"
@@ -381,9 +377,7 @@ def test_context_show_acms_config() -> None:
     if not isinstance(limits, dict):
         raise AssertionError(f"Missing limits in payload: {payload.keys()}")
     if limits.get("hot_max_tokens") != 5000:
-        raise AssertionError(
-            f"hot_max_tokens mismatch: {limits.get('hot_max_tokens')}"
-        )
+        raise AssertionError(f"hot_max_tokens mismatch: {limits.get('hot_max_tokens')}")
 
     if "summarization" not in payload:
         raise AssertionError(