Add coding-agent guidance and llms.txt decision rules

[autocarl]

Summary

• Adds a new For Coding Agents guide with decision rules, minimal implementation snippets, MCP guidance, structured-output guidance, and copy/paste AGENTS.md / CLAUDE.md / Cursor / Cline instructions.
• Updates llms.txt so agent-readable entry points include the new guide, explicit decision rules, common agent tasks, and the Repl.Mcp wording clarification.
• Clarifies across MCP docs that Repl.Mcp is the component used to build MCP servers; the app built with Repl is the server an agent host launches.
• Aligns the site MCP cookbook with yllibed/repl#37: build local samples first, then use dotnet run --no-build --project ... -- mcp serve in host configs.
• Documents VS Code/Copilot's .vscode/mcp.json shape separately with top-level servers while keeping mcpServers for Cursor/Cline/Claude-style clients.

Refs yllibed/repl#36.

Verification

• git diff --check origin/main...HEAD — passed.
• git diff --check — passed.
• Fragile host-pattern scan for dotnet run --project without --no-build — passed.
• JSON parsing of both cookbook host config snippets (mcpServers and VS Code servers) — passed.
• ASTRO_TELEMETRY_DISABLED=1 XDG_CONFIG_HOME=/workspace/.config npm run astro -- build — passed, including /cookbook/mcp-server/ and /getting-started/for-coding-agents/.
• Full npm run build was previously attempted locally, but DocFX metadata generation failed against the local checked-out Repl source before Astro build.
• gh pr checks reports no checks on the branch. Current workflow triggers are push to main, workflow_dispatch, repository_dispatch, and scheduled deploy; there is no pull_request CI trigger in this repo yet.

[carldebilly]

@codex Please review this and correlate with the content of yllibed/repl#37

[chatgpt-codex-connector]

💡 Codex Review

Here are some automated review suggestions for this pull request.

Reviewed commit: 77ca7e8c37

ℹ️ About Codex in GitHub

Your team has set up Codex to review pull requests in this repo. Reviews are triggered when you

• Open a pull request for review
• Mark a draft as ready
• Comment "@codex review".

If Codex has suggestions, it will comment; otherwise it will react with 👍.

Codex can also answer questions or update the PR. Try commenting "@codex address that feedback".

[autocarl]

@codex please review this updated PR and correlate it with yllibed/repl#37.

[carldebilly]

@codex please review this again.

[chatgpt-codex-connector]

💡 Codex Review

Here are some automated review suggestions for this pull request.

Reviewed commit: c6dcfc1d02

ℹ️ About Codex in GitHub

Your team has set up Codex to review pull requests in this repo. Reviews are triggered when you

• Open a pull request for review
• Mark a draft as ready
• Comment "@codex review".

If Codex has suggestions, it will comment; otherwise it will react with 👍.

Codex can also answer questions or update the PR. Try commenting "@codex address that feedback".