Add Perplexity as a model provider

[jliounis]

Summary

Adds Perplexity as a first-class model provider in Aider, mirroring the OpenRouter integration pattern. Perplexity exposes an OpenAI-compatible Agent API at https://api.perplexity.ai, which LiteLLM already supports under the perplexity/ provider prefix.

The default model in all examples is perplexity/sonar-pro.

Files changed

• aider/website/docs/llms/perplexity.md — new provider docs page (mirrors openrouter.md)
• aider/resources/model-settings.yml — model entries for sonar, sonar-pro, sonar-reasoning, sonar-reasoning-pro, sonar-deep-research
• aider/onboarding.py — PERPLEXITY_API_KEY → perplexity/sonar-pro in default-model auto-selection
• aider/models.py — perplexity provider added to fast_validate_environment keymap
• tests/basic/test_onboarding.py — coverage for Perplexity env-var detection
• tests/basic/test_models.py — coverage for the new model-settings entries

Available models

• perplexity/sonar
• perplexity/sonar-pro (default)
• perplexity/sonar-reasoning
• perplexity/sonar-reasoning-pro
• perplexity/sonar-deep-research

Test plan

• pytest tests/basic/test_onboarding.py tests/basic/test_models.py — all pass
• Full tests/basic/ suite passes (only the pre-existing test_voice.py failures from this sandbox's missing sound device are unrelated)
• aider --model perplexity/sonar-pro resolves the new model settings

References: https://docs.perplexity.ai

[CLAassistant]

Thank you for your submission! We really appreciate it. Like many open source projects, we ask that you sign our Contributor License Agreement before we can accept your contribution.

---

james-pplx seems not to be a GitHub user. You need a GitHub account to be able to sign the CLA. If you have already a GitHub account, please add the email address used for this commit to your account.
_{You have signed the CLA already but the status is still pending? Let us recheck it.}