feat(tts): add pocket-tts backend

[mudler]

Description

This PR adds the new pocket-tts backend (https://kyutai.org/blog/2026-01-13-pocket-tts).

Note, for voice cloning it requires to login via HF, which is a manual process at the moment.

Notes for Reviewers

Signed commits

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[github-actions]

yamllint Failed

Show Output

::group::backend/index.yaml
::warning file=backend/index.yaml,line=106,col=6::106:6 [comments] missing starting space in comment
::warning file=backend/index.yaml,line=990,col=6::990:6 [comments] missing starting space in comment
::warning file=backend/index.yaml,line=1246,col=3::1246:3 [comments-indentation] comment not indented like content
::error file=backend/index.yaml,line=1712,col=74::1712:74 [new-line-at-end-of-file] no new line character at the end of file
::endgroup::

Workflow: Yamllint GitHub Actions, Action: __karancode_yamllint-github-action_2, Lint: backend