Document ElevenLabs provider

[tanish19078]

Summary

• Add a dedicated ElevenLabs provider documentation page covering API-key setup, environment variables, API endpoint, and displayed usage fields.
• Link ElevenLabs from the README provider list and the provider strategy overview.
• Add ElevenLabs to the static docs homepage provider grid and refresh the provider count metadata.

Verification

• node Scripts/docs-list.mjs
• git diff --cached --check

[steipete]

Thanks @tanish19078, landed this on main.

I recreated the docs patch locally because this PR branch has maintainer edits disabled, then added the CLI codexbar config set-api-key --provider elevenlabs --stdin flow and updated the README social alt provider count too.

Landed commits:

• f6a0f7044b9acaa530579195b33550a56dfb808c — your ElevenLabs docs patch, with authorship preserved
• 8c29b3b89da77102b5b40bbd3669474aa84044ce — maintainer polish for the CLI setup docs

Verified with:

• node Scripts/docs-list.mjs
• git diff --check HEAD~1 HEAD
• git diff --check
• codex-review --mode branch