docs: create deepseek harness plugin docs

[daveomri]

Add DeepSeek Harness integration doc

Documents the Apify plugin for DeepSeek Harness: installing it into a dsh profile, authenticating with APIFY_TOKEN via a .env file, connecting a model provider, and the five bundled workflow skills.

• sources/platform/integrations/ai/deepseek-harness.md - new page, following the Kimi Code CLI structure
• static/img/platform/integrations/deepseek.svg - vendor mark, brand blue as an explicit fill, so no dark variant is needed
• Cards added to the AI hub and the top-level integrations hub

DeepSeek Harness has no OAuth flow for MCP servers and sandboxes file access, so the doc covers the token-only auth path and the EPERM the Apify CLI hits under the default sandbox mode.

markdownlint and vale --minAlertLevel=error pass on the new page.

🤖 Generated with Claude Code