docs: add Nika to Agentic Libraries & Assistants integrations

[ThibautMelen]

Adds Nika to Community Integrations → Agentic Libraries & Assistants.

Nika is an intent-as-code workflow engine in a single Rust binary (AGPL-3.0), and LocalAI is a first-class local provider in its catalog — model: localai/<name> works out of the box (verified against the shipped binary: nika doctor lists localai among the five local providers, and a localai/... workflow passes nika check). Workflows are reviewable YAML DAGs audited for schema, permits and an honest cost floor before any token is spent.

Disclosure: I'm Nika's author.

[localai-bot]

Thanks for adding Nika, and for the disclosure. Two small things before this can go in:

1. The DCO check is failing. Please sign off the commit (git commit --amend -s and force-push to your branch) so the Developer Certificate of Origin check passes.
2. Could you shorten the description to match the neighboring entries? They are one short phrase each (for example 'Agentic library for Go'). Something like: Intent-as-code AI workflow engine in a single Rust binary, with LocalAI as a built-in local provider. The extra detail about schema checks and cost auditing fits better in Nika's own README.

Placement in Agentic Libraries & Assistants is right and even keeps the list alphabetical, so after those two tweaks this should be an easy merge.