Add Gravitee as a supported AI Gateway

[samprodger]

Summary

• Adds Gravitee AI Gateway to the gateway logo grid on the Models & Credentials page, alongside the other OpenAI-/Anthropic-compatible gateways already listed (Portkey, Cloudflare, Kong, etc.)
• Adds a base-URL/key example row for Gravitee to the config table, matching the OpenRouter/Ollama rows already there
• Adds a short note pointing to Gravitee's LLM Proxy docs, and clarifies that Omnigent delivers the configured key to Claude Code via apiKeyHelper, so the Gravitee API's security plan should accept that credential the same way any API-key gateway would
• Updates the corresponding text in scripts/generate-llms-files.mjs and hand-patches the already-committed public/llms-full.txt so the crawler-facing docs stay in sync with the human-facing page (scoped to just this paragraph — the checked-in llms-full.txt has some unrelated drift from other pages that I left untouched rather than bundling in a much bigger regeneration diff)

No code changes needed on Omnigent's side — the Gateway credential type is already a generic OpenAI-/Anthropic-compatible client (base_url + key from the agent YAML), so this is a docs-only PR.

Test plan

• Confirm the new logo renders correctly at /docs/build/models
• Confirm the table and note render as expected in the MDX
• Swap public/logos/gateways/gravitee.png for an official brand asset if preferred — current one is Gravitee's GitHub org avatar, resized to 80x80 to match the existing logo set

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