fix(plugins): remove broken mcpServers references that broke plugin loading

The MCP consolidation commit (afd4c44) deleted plugin-level .mcp.json files
but left references to them in plugin.json and marketplace.json. This caused
7 plugins to fail loading (projman, pr-review, cmdb-assistant, data-platform,
viz-platform, contract-validator, and indirectly git-flow/clarity-assist).

Changes:
- Remove mcpServers field from 6 plugin.json files (file no longer exists)
- Remove mcpServers field from 6 marketplace.json entries
- Add file reference validation to validate-marketplace.sh:
  - Validates mcpServers references point to existing files
  - Validates hooks references point to existing files
  - Validates commands references point to existing paths
- Add pre-commit hook (.git/hooks/pre-commit) to enforce validation

The validation script will now FAIL if any config file references a
non-existent file, preventing this class of bug from happening again.

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

.claude-plugin/marketplace.json

@@ -20,7 +20,6 @@
       },
       "homepage": "https://gitea.hotserv.cloud/personal-projects/leo-claude-mktplace/src/branch/main/plugins/projman/README.md",
       "repository": "https://gitea.hotserv.cloud/personal-projects/leo-claude-mktplace.git",
-      "mcpServers": ["./.mcp.json"],
       "category": "development",
       "tags": ["sprint", "agile", "gitea", "project-management"],
       "license": "MIT"
@@ -84,7 +83,6 @@
       },
       "homepage": "https://gitea.hotserv.cloud/personal-projects/leo-claude-mktplace/src/branch/main/plugins/cmdb-assistant/README.md",
       "repository": "https://gitea.hotserv.cloud/personal-projects/leo-claude-mktplace.git",
-      "mcpServers": ["./.mcp.json"],
       "category": "infrastructure",
       "tags": ["cmdb", "netbox", "dcim", "ipam", "data-quality", "validation"],
       "license": "MIT"
@@ -145,7 +143,6 @@
       },
       "homepage": "https://gitea.hotserv.cloud/personal-projects/leo-claude-mktplace/src/branch/main/plugins/pr-review/README.md",
       "repository": "https://gitea.hotserv.cloud/personal-projects/leo-claude-mktplace.git",
-      "mcpServers": ["./.mcp.json"],
       "category": "development",
       "tags": ["code-review", "pull-requests", "security", "quality"],
       "license": "MIT"
@@ -161,7 +158,6 @@
       },
       "homepage": "https://gitea.hotserv.cloud/personal-projects/leo-claude-mktplace/src/branch/main/plugins/data-platform/README.md",
       "repository": "https://gitea.hotserv.cloud/personal-projects/leo-claude-mktplace.git",
-      "mcpServers": ["./.mcp.json"],
       "category": "data",
       "tags": ["pandas", "postgresql", "postgis", "dbt", "data-engineering", "etl"],
       "license": "MIT"
@@ -177,7 +173,6 @@
       },
       "homepage": "https://gitea.hotserv.cloud/personal-projects/leo-claude-mktplace/src/branch/main/plugins/viz-platform/README.md",
       "repository": "https://gitea.hotserv.cloud/personal-projects/leo-claude-mktplace.git",
-      "mcpServers": ["./.mcp.json"],
       "category": "visualization",
       "tags": ["dash", "plotly", "mantine", "charts", "dashboards", "theming", "dmc"],
       "license": "MIT"
@@ -193,7 +188,6 @@
       },
       "homepage": "https://gitea.hotserv.cloud/personal-projects/leo-claude-mktplace/src/branch/main/plugins/contract-validator/README.md",
       "repository": "https://gitea.hotserv.cloud/personal-projects/leo-claude-mktplace.git",
-      "mcpServers": ["./.mcp.json"],
       "category": "development",
       "tags": ["validation", "contracts", "compatibility", "agents", "interfaces", "cross-plugin"],
       "license": "MIT"