fix: accept trailing slash endpoints

[EfeDurmaz16]

Summary

Allows MCP endpoint matching to tolerate trailing slash redirects, e.g. /mcp/ when Next.js trailingSlash is enabled.

Fixes #143.

Changes

• Normalize request pathnames before comparing them with configured MCP endpoints
• Preserve root path behavior
• Apply the same normalization to streamable HTTP, SSE, and SSE message endpoints
• Add unit coverage for trailing slash normalization

Verification

• pnpm install --frozen-lockfile
• pnpm test tests/mcp.test.ts
• pnpm build
• git diff --check