fix(marketplace): remove integrates_with field (schema violation)

Claude Code's marketplace schema does not support custom fields.
The `integrates_with` field on data-platform and viz-platform caused:
"Invalid schema: plugins.9: Unrecognized key: integrates_with"

This reverts the schema extension while keeping the validate_workflow_integration
MCP tool functional (it reads from plugin.json files directly, not marketplace.json).

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

.claude-plugin/marketplace.json

@@ -167,15 +167,7 @@
       "hooks": ["./hooks/hooks.json"],
       "category": "data",
       "tags": ["pandas", "postgresql", "postgis", "dbt", "data-engineering", "etl"],
-      "license": "MIT",
-      "integrates_with": {
-        "projman": {
-          "domain_label": "Domain/Data",
-          "gate_command": "/data-gate",
-          "review_command": "/data-review",
-          "advisory_agent": "data-advisor"
-        }
-      }
+      "license": "MIT"
     },
     {
       "name": "viz-platform",
@@ -191,15 +183,7 @@
       "hooks": ["./hooks/hooks.json"],
       "category": "visualization",
       "tags": ["dash", "plotly", "mantine", "charts", "dashboards", "theming", "dmc"],
-      "license": "MIT",
-      "integrates_with": {
-        "projman": {
-          "domain_label": "Domain/Viz",
-          "gate_command": "/design-gate",
-          "review_command": "/design-review",
-          "advisory_agent": "design-reviewer"
-        }
-      }
+      "license": "MIT"
     },
     {
       "name": "contract-validator",