Agent marks for the /ai connector tabs

Each tab in the "connect your own agent" section renders client.logo when it is set in src/ai.njk, and falls back to the agent's name as text when it is not.

File Tab Source
microsoft-copilot.svg Microsoft Copilot adoption.microsoft.com/wp-content/uploads/2023/09/icon-copilot.svg, a Microsoft-owned domain. Still needs a legal check: Microsoft's trademark guidelines generally require permission to use its marks in a way that presents a product relationship, and this came from a marketing page rather than a brand kit with usage terms attached.
chatgpt.svg ChatGPT OpenAI brand kit, OAI_OpenAI-Blossom_Black.svg, downloaded by hand from openai.com/brand because that page blocks automated fetching. This is the OpenAI symbol, which is the icon form their kit provides.
claude.svg Claude Anthropic press kit, anthropic.com/press-kit, which redirects to an official CDN zip. File is "Claude Spark - Clay", the icon form intended to sit beside a label. Unmodified, in its own brand colour.
gemini.svg Gemini Google's own CDN, the Gemini sparkle used by Gemini's product surfaces.
(none) Local and Custom Agents Not a brand mark by design. The repo icon components/icons/server-stack.svg is inlined instead of linked as a file, so it inherits currentColor and turns white when the tab is active.

All marks are used unmodified, at their own aspect ratio, in a 16px-tall slot beside the agent's name. None is altered in colour or proportion.

To add or replace one, drop the file here and set the path on that client:

        - id: "claude"
logo: "/images/ai/agents/claude.svg"

Leave logo unset until the file exists. Setting it early renders a broken image, whereas leaving it unset renders the name as text, which is the intended fallback.