docs: list OpenCode in CLAUDE.md supported-agent set (#924)

Follow-up to #923 (OpenCode agent-install support). The user-facing
README and CLI help were reconciled there; this brings the dev-guide's
supported-agent enumeration in line too.

Claude-Session: https://claude.ai/code/session_015yuBJQYfDj95cgX3DaD8SF

Author: xarmian

CLAUDE.md

@@ -2,7 +2,7 @@
 
 ## What This Is
 
-Pad is a project management tool for developers and AI agents. Single Go binary with embedded SvelteKit web UI, SQLite storage, and multi-agent skill support (Claude Code, Cursor, Windsurf, Codex, Copilot, Amazon Q, Junie).
+Pad is a project management tool for developers and AI agents. Single Go binary with embedded SvelteKit web UI, SQLite storage, and multi-agent skill support (Claude Code, Cursor, Windsurf, Codex, OpenCode, Copilot, Amazon Q, Junie).
 
 **Related repo:** The marketing website (getpad.dev) lives at `../pad-web` — a separate SvelteKit site deployed to Vercel.