docs: add Kesha voice backend

[drakulavich]

Summary

• add Kesha Voice Kit to ECOSYSTEM.md as a local Hermes STT/TTS command-provider backend
• link the dedicated Kesha Hermes setup guide with copy-paste HERMES_LOCAL_STT_COMMAND and tts.providers config

Validation

• git diff --check

[devin-ai-integration]

Reviewed and verified — this is ready to merge.

• The two Hermes config primitives it documents are real: HERMES_LOCAL_STT_COMMAND is in the official env-var reference, and tts.providers.<name>.type: command is the command-type TTS provider (landed upstream in feat(tts): add command-type provider registry under tts.providers.<name> NousResearch/hermes-agent#17843).
• Both new links resolve, and markdown-link-check passes on the modified ECOSYSTEM.md (53/53 links).
• Placement and descriptive (non-promotional) tone match CONTRIBUTING.md; no conflicts with main.

Heads up: GitHub hasn't run the CI workflow on this fork PR yet (it needs a maintainer to approve the workflow run for a first-time contributor). Once you approve the run it should go green. I'm not able to merge into main myself — over to you to merge.