feat(viz-platform): create plugin structure (#177)

- Add plugins/viz-platform/ directory structure
- Create .claude-plugin/plugin.json with metadata
- Create .mcp.json pointing to viz-platform MCP server
- Create hooks/hooks.json with SessionStart hook
- Create symlink to mcp-servers/viz-platform
- Add plugin to marketplace.json

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

plugins/viz-platform/.mcp.json

@@ -0,0 +1,10 @@
+{
+  "mcpServers": {
+    "viz-platform": {
+      "type": "stdio",
+      "command": "${CLAUDE_PLUGIN_ROOT}/mcp-servers/viz-platform/.venv/bin/python",
+      "args": ["-m", "mcp_server.server"],
+      "cwd": "${CLAUDE_PLUGIN_ROOT}/mcp-servers/viz-platform"
+    }
+  }
+}