Add Tura as an open-source coding agent

Following [CONTRIBUTING_TO_OSB.md](https://github.com/junaid33/opensource.builders/blob/master/CONTRIBUTING_TO_OSB.md), I would like to submit a standalone open-source development tool.

Add open source tool: Tura
- Repository: https://github.com/Tura-AI/tura
- Website: https://turaai.net/
- Description: A local, open-source coding agent with CLI, TUI, desktop, and optional web interfaces. It uses structured macro command execution to reduce repeated model round trips and supports configurable agents and task-scoped runtime state.
- Category: Development Tools
- Features: Local/self-hosted operation, CLI and TUI workflows, desktop and optional web UI, multi-session work, custom agents, task checkpoints and context compaction, Ollama and custom OpenAI-compatible providers

## Additional information

- License: AGPL-3.0-or-later
- Primary language: Rust
- Documentation: https://github.com/Tura-AI/tura#readme
- Published benchmark methodology and evidence: https://turaai.net/benchmark
- Related technical article: https://turaai.net/blog#token-saving-plugins-are-mostly-stupid-idea

Disclosure: I am submitting this on behalf of the Tura project.

Start with CONTRIBUTING_TO_OSB.md and inspect how existing development tools are represented in the repository. Add Tura using the supplied repository, website, description, category, features, license, language, and documentation links, then verify that the listing is complete and follows the project’s contribution format.

Written by the indexing model from the issue text.