fix(cli): address PR #6626 review blockers for context set output

- Fix ruff import ordering in project_context_cli_steps.py (yaml moved to third-party section)
- Remove unused noqa: F401 suppression in rendering/__init__.py
- Add *args, **kwargs to _test_format_output stub in coverage boost steps (fixes TypeError)
- Extract context-set step definitions into dedicated module (project_context_set_steps.py)
  to bring project_context_cli_steps.py under 500-line limit (469 -> 316 lines)
- Revert spec changes for context show/inspect/simulate message format (bare strings)
  to keep PR focused on issue #6319 (context set only),

docs/specification.md

@@ -4156,9 +4156,7 @@ Show the active context policy for a project.
       "timing": {
         "duration_ms": 38
       },
-      "messages": [
-        {"level": "ok", "text": "Context policy loaded"}
-      ]
+      "messages": ["Context policy loaded"]
     }
     ```
 
@@ -4197,8 +4195,7 @@ Show the active context policy for a project.
     timing:
       duration_ms: 38
     messages:
-      - level: ok
-        text: Context policy loaded
+      - Context policy loaded
     ```
 
 ###### agents project context inspect
@@ -4347,9 +4344,7 @@ Inspect the current state of the ACMS context assembly for a project. Shows the
       "timing": {
         "duration_ms": 185
       },
-      "messages": [
-        {"level": "ok", "text": "Context inspection complete"}
-      ]
+      "messages": ["Context inspection complete"]
     }
     ```
 
@@ -4416,8 +4411,7 @@ Inspect the current state of the ACMS context assembly for a project. Shows the
     timing:
       duration_ms: 185
     messages:
-      - level: ok
-        text: Context inspection complete
+      - Context inspection complete
     ```
 
 ###### agents project context simulate
@@ -4581,12 +4575,7 @@ Simulate a context assembly run without invoking an actor. Produces a dry-run re
       "timing": {
         "duration_ms": 310
       },
-      "messages": [
-        {
-          "level": "ok",
-          "text": "Simulation complete (dry run -- no context was assembled)"
-        }
-      ]
+      "messages": ["Simulation complete (dry run -- no context was assembled)"]
     }
     ```
 
@@ -4654,8 +4643,7 @@ Simulate a context assembly run without invoking an actor. Produces a dry-run re
     timing:
       duration_ms: 310
     messages:
-      - level: ok
-        text: Simulation complete (dry run -- no context was assembled)
+      - "Simulation complete (dry run -- no context was assembled)"
     ```
 
 #### agents actor