simpleStreamableHttp: fix example code

[ochafik]

Update simpleStreamableHttp.ts example so its in-memory OAuth server isn't always strict (only make it strict if --oauth-strict isn't passed).

Follow up to #638 cc/ @pcarleton

Motivation and Context

While testing an old inspector's refresh flow w/ the new simpleStreamableHttp.ts, realized the in-memory oauth is too strict. This loosens it unless --oauth-strict is set.

How Has This Been Tested?

Using a pre-resources inspector (before modelcontextprotocol/inspector#526) + new typescript-sdk (after #638):

git clone https://github.com/modelcontextprotocol/typescript-sdk
( cd typescript-sdk && npx tsx src/examples/server/simpleStreamableHttp.ts  --oauth )& # no need for --oauth-strict here

git clone https://github.com/modelcontextprotocol/inspector
( cd inspector && npm run dev http://localhost:3000/mcp )

# Then:
# - Connect to the MCP server in the inspector (works),
# - Open the Auth panel
# - Click "Quick Refresh": fails!
# - Server console output says: "Invalid resource: undefined"

Breaking Changes

None (just better example in main branch)

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)
• Documentation update (the example being a form of documentation)

[pcarleton]

nice lgtm