Add Oats to Tauri list

[mchlggr]

What does this PR do?

Adds Oats to Open Source > Tauri. Oats is an MIT-licensed local-first macOS meeting-notes app with live transcription, speaker labels, AI summaries, and a fully offline on-device mode.

Checklist

• I have read the contribution guidelines
• The entry follows the documented entry format
• The tool is not already on the list
• The tool is actively maintained (last commit within 12 months)
• Icons are accurate (checked platform support, sync, encryption)
• The link works and points to the official source
• For open-source tools: license (SPDX) and tech stack are included
• Added to the correct category

Validation

• git diff --check
• npm exec --yes --package markdownlint-cli@0.45.0 -- markdownlint README.md