## Summary
Making thread id optional so that we can better cache resources for MCPs
for connectors since their resource templates is universal and not
particular to projects.
- Make `mcpServer/resource/read` accept an optional `threadId`
- Read resources from the current MCP config when no thread is supplied
- Keep the existing thread-scoped path when `threadId` is present
- Update the generated schemas, README, and integration coverage
## Testing
- `just write-app-server-schema`
- `just fmt`
- `cargo test -p codex-app-server-protocol`
- `cargo test -p codex-mcp`
- `cargo test -p codex-app-server --test all mcp_resource`
- `just fix -p codex-mcp`
- `just fix -p codex-app-server-protocol`
- `just fix -p codex-app-server`
