feat: add MCP servers dashboard page with CRUD and token management

New page at /mcp-servers to register, view, and manage MCP server
instances. Shows endpoint config, enabled tools, and access tokens
with reveal/regenerate controls. Includes McpServerConfig model in
compliance-core, MongoDB collection accessor, server functions for
list/add/delete/regenerate-token, sidebar nav entry, and full CSS.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

compliance-dashboard/src/infrastructure/database.rs

@@ -42,4 +42,8 @@ impl Database {
     pub fn tracker_issues(&self) -> Collection<TrackerIssue> {
         self.inner.collection("tracker_issues")
     }
+
+    pub fn mcp_servers(&self) -> Collection<McpServerConfig> {
+        self.inner.collection("mcp_servers")
+    }
 }