docs: add WaveSpeed AI provider page

[chengzeyi]

Adds a provider page for WaveSpeed AI covering image generation, video generation and the OpenAI-compatible chat endpoint, with SDK and proxy examples for each surface plus the supported parameter tables. It also explains how the asynchronous prediction API maps onto each one: LiteLLM polls internally for images, while video generation returns a task id and you drive video_status and video_content yourself.

WAVESPEED_API_KEY and WAVESPEED_API_BASE are added to the environment variables reference in docs/proxy/config_settings.md, and the page is registered in sidebars.js after the WatsonX category.

This is the docs half of BerriAI/litellm#37627, which adds the provider itself. That PR is currently red on code-quality and documentation, both because tests/documentation_tests/test_env_keys.py reports WAVESPEED_API_BASE and WAVESPEED_API_KEY as read under ./litellm but documented nowhere; merging this fixes both. It also makes the https://docs.litellm.ai/docs/providers/wavespeed link that the code PR registers in provider_endpoints_support.json resolve instead of 404.

Verified by checking out this branch into docs/my-website of the code PR's branch and running the four documentation tests the CI jobs run, all of which pass:

test_env_keys exit=0
test_router_settings exit=0
test_api_docs exit=0
test_circular_imports exit=0

npm run build also succeeds and emits build/docs/providers/wavespeed/index.html. The build reports broken links, but every one of them is pre-existing on other pages; none are on or point to the new page.

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Project	Deployment	Actions	Updated (UTC)
litellm	Ready	Preview	Aug 20, 2026 12:35pm

[chengzeyi]

Cross-linking: BerriAI/litellm#37627 is blocked on this PR. Its code-quality and documentation jobs check out this repo's default branch into docs/my-website (no ref), then fail with Environment variables read under ./litellm but mentioned nowhere in the docs: ['WAVESPEED_API_BASE', 'WAVESPEED_API_KEY']. The rows added here are what satisfy that check — every other check on #37627 is green.