fix: revert changes to 2025-03-26 spec

Author: kurtisvg

docs/specification/2025-03-26/basic/authorization.mdx

@@ -132,7 +132,15 @@ sequenceDiagram
     Note over C: Continue with authorization flow
 ```
 
-#### 2.3.1 Authorization Base URL
+#### 2.3.1 Server Metadata Discovery Headers
+
+MCP clients _SHOULD_ include the header `MCP-Protocol-Version: <protocol-version>` during
+Server Metadata Discovery to allow the MCP server to respond based on the MCP protocol
+version.
+
+For example: `MCP-Protocol-Version: 2024-11-05`
+
+#### 2.3.2 Authorization Base URL
 
 The authorization base URL **MUST** be determined from the MCP server URL by discarding
 any existing `path` component. For example:
@@ -146,7 +154,7 @@ If the MCP server URL is `https://api.example.com/v1/mcp`, then:
 This ensures authorization endpoints are consistently located at the root level of the
 domain hosting the MCP server, regardless of any path components in the MCP server URL.
 
-#### 2.3.2 Fallbacks for Servers without Metadata Discovery
+#### 2.3.3 Fallbacks for Servers without Metadata Discovery
 
 For servers that do not implement OAuth 2.0 Authorization Server Metadata, clients
 **MUST** use the following default endpoint paths relative to the authorization base URL