docs: add OpenCode Desktop integration guide

[analogpvt]

Summary

• Adds full OpenCode Desktop integration guide at apps/docs/content/guides/opencode-desktop.mdx with 5 screenshots covering provider setup, API key entry, model selection, and active chat
• Adds OpenCode Desktop card to the integrations page in apps/ui (uses existing OpenCodeIcon, links to docs)
• Adds markdown copy at apps/ui/src/content/guides/opencode-desktop.md for the UI slug page
• Copies 5 guide images to both apps/docs/public/guides/opencode-desktop/ and apps/ui/public/images/guides/opencode-desktop/

Test plan

• apps/docs: OpenCode Desktop guide renders at /guides/opencode-desktop with all 5 screenshots visible
• apps/ui: OpenCode Desktop card appears on /guides page and links to https://docs.llmgateway.io/guides/opencode-desktop
• apps/ui: /guides/opencode-desktop slug page renders the markdown content with images
• Images render correctly on GitHub (relative paths)
• pnpm --filter docs build passes with no errors

🤖 Generated with Claude Code

Summary by CodeRabbit

Release Notes

• Documentation

  • Added comprehensive integration guides for OpenCode Desktop, including setup instructions, prerequisites, model configuration, and troubleshooting.

• New Features

  • Added OpenCode Desktop as a distinct integration option in the product UI.

[coderabbitai]

No actionable comments were generated in the recent review. 🎉

ℹ️ Recent review info

⚙️ Run configuration

Configuration used: Repository UI

Review profile: CHILL

Plan: Pro

Run ID: b2cfd7c3-dd12-4fa9-8cfd-5b79dae256d1

📥 Commits

Reviewing files that changed from the base of the PR and between 25003ac and 8877edc.

📒 Files selected for processing (1)

• apps/ui/src/components/integrations/integration-cards.tsx

✅ Files skipped from review due to trivial changes (1)

• apps/ui/src/components/integrations/integration-cards.tsx

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Walkthrough

This PR adds documentation for integrating OpenCode Desktop with LLM Gateway (two parallel guide files: MDX and plain markdown), and updates the integration cards UI to distinguish OpenCode CLI and add a new OpenCode Desktop entry linking to the new guides.

Changes

OpenCode Desktop Integration Documentation

Layer / File(s)	Summary
Main UI Documentation Guide apps/ui/src/content/guides/opencode-desktop.md	Frontmatter metadata, prerequisites (OpenCode Desktop + API key), platform-specific installation steps, five-step setup flow (Providers settings, locate gateway, enter API key, select model, start chat), feature list, model switching instructions, and troubleshooting sections for provider visibility, authentication, and model loading.
Fumadocs Structured Documentation apps/docs/content/guides/opencode-desktop.mdx	MDX-based guide with frontmatter, imported UI components (Steps, Callout), mirrors the main guide with info/warning callouts, adds opencode.json example for provider locking via X-No-Fallback header, and styled troubleshooting sections.
Integration Card Navigation apps/ui/src/components/integrations/integration-cards.tsx	Clarifies existing "OpenCode" entry as "OpenCode CLI" and adds new "OpenCode Desktop" integration card linking to the desktop documentation with identical icon and available status.

Estimated code review effort

🎯 3 (Moderate) | ⏱️ ~20 minutes

Possibly related PRs

• theopenco/llmgateway#2263: Modifies the same integration cards component to add or update integration entries.

Suggested reviewers

• smakosh

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title accurately describes the main change: adding a comprehensive OpenCode Desktop integration guide across documentation and UI files.
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check.
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.

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✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests

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