#15356: fix: adding Together AI provider to docs

### Summary Adds support for **Together AI** as a new provider in the documentation, integrating it into both the provider list and models reference page. ### Changes - Added `"providers/together"` to the list of supported providers in `docs.json`. - Included a new entry for **Together AI** in the models documentation (`providers/models.md`) with a link to its dedicated page. <!-- greptile_comment --> <h2>Greptile Overview</h2> <h3>Greptile Summary</h3> This PR updates the documentation navigation and provider quickstart list to include **Together AI**: - Adds `providers/together` to the Models → Providers navigation in `docs/docs.json`. - Adds a Together AI link to the supported providers list in `docs/providers/models.md`. This keeps the provider quickstart and docs navigation aligned with the existing provider doc at `docs/providers/together.md`. <h3>Confidence Score: 5/5</h3> - This PR is safe to merge with minimal risk. - The changes are limited to docs navigation and a single markdown link addition. The referenced route `/providers/together` is backed by an existing `docs/providers/together.md`, and there are no code/runtime changes. - No files require special attention _{Last reviewed commit: bcdd026} <!-- greptile_other_comments_section --> **Context used:** - Context from `dashboard` - CLAUDE.md ([source](https://app.greptile.com/review/custom-context?memory=fd949e91-5c3a-4ab5-90a1-cbe184fd6ce8)) - Context from `dashboard` - AGENTS.md ([source](https://app.greptile.com/review/custom-context?memory=0d0c8278-ef8e-4d6c-ab21-f5527e322f13)) <!-- /greptile_comment -->