[plan] Add engine feature comparison table to engines reference docs

[github-actions]

Context

From discussion #21966 (Repository Quality Report: AI Engine Feature Parity).

Objective

The docs/src/content/docs/reference/engines.md page describes each engine but lacks a feature comparison table. Users cannot easily determine which capabilities (max-turns, max-continuations, plugins, web-search, web-fetch, tools allowlist) are available for each engine without reading engine-specific code.

Approach

1. Open docs/src/content/docs/reference/engines.md
2. Add a ## Engine Feature Support section after the "## Available Coding Agents" engine table
3. Include a feature comparison table based on the actual Supports*() methods:

Feature	Copilot	Claude	Codex	Gemini
max-turns	❌	✅	❌	❌
max-continuations	✅	❌	❌	❌
plugins	✅	❌	❌	❌
web-search (built-in)	❌	✅	✅	❌
web-fetch (built-in)	✅	✅	❌	❌
Tools allowlist	✅	✅	✅	✅

4. Add brief notes below the table explaining features that require special configuration
5. Follow the existing docs style (GitHub-flavored Markdown, Astro Starlight conventions)
6. Do NOT change the page title or frontmatter

Files to Modify

• docs/src/content/docs/reference/engines.md

Acceptance Criteria

• A feature comparison table is added showing all 4 engines × 6 capabilities
• Table values match the Supports*() method return values in the engine constructors
• Brief notes explain any feature that requires special config or has engine-specific limitations
• Docs style is consistent with existing content

Generated by Plan Command for issue #discussion #21966 · ◷

• expires on Mar 23, 2026, 3:32 PM UTC