docs(langsmith): document signing JWKS setup

[Mukil Loganathan (langchain-infra)]

Summary

• Documents signing JWKS setup in the existing Kubernetes installation guide as the canonical instructions for self-hosted OAuth login, Remote MCP, and the LLM auth proxy.
• Corrects the Helm 0.16.0 configuration paths: config.signingJwks or the lowercase langsmith_signing_jwks key in the chart-wide existing Secret.
• Explains the upgrade requirement to remove LANGSMITH_SIGNING_JWKS from extra environment variables and restart platform-backend after external Secret-only updates.
• Links each feature-specific guide to the shared Kubernetes instructions.

Test Plan

• Generated a throwaway Ed25519 JWKS with the documented commands and verified its structure.
• Validated the documented configurations against the Helm 0.16.0 JWKS test suite (12/12 scenarios passed).
• Ran the documentation cross-reference check and full build.

[github-actions]

Thanks for opening a docs PR, Mukil Loganathan (@langchain-infra)! When it's ready for review, please add the relevant reviewers:

• @fjmorris or @lnhsingh (LangSmith)

[github-actions]

Mintlify preview branch generated: preview-codexf-1788227809-773f4d5

Site preview: https://langchain-5e9cc07a-preview-codexf-1788227809-773f4d5.mintlify.site

Important

Preview links may take a few minutes to start working while the deployment finishes.

Changed documentation pages (preview deep links):

• src/langsmith/kubernetes.mdx
• src/langsmith/llm-auth-proxy-self-hosted.mdx
• src/langsmith/langsmith-remote-mcp.mdx
• src/langsmith/self-host-using-an-existing-secret.mdx
• src/langsmith/langsmith-cli.mdx

Only the top 5 changed markdown files by diff size are listed.