feat: add Zed editor to IDE tools / compatibility table

[reealk]

What

Add Zed to the compatibility table and installation instructions as a supported editor.

Why

Zed is a fast, modern code editor with native AI integration (Agent Panel, Inline Assistant). It already reads the same context files as other supported tools:

• CLAUDE.md — auto-included in all Agent Panel interactions
• AGENTS.md — project-level instructions
• GEMINI.md — recognized natively

Since AIDD writes rules to CLAUDE.md / AGENTS.md, Zed works out of the box. Adding it to the compatibility table makes this explicit for users.

Zed also supports Skills (reusable instruction packages) loaded from ~/.agents/skills/ (global) or <worktree>/.agents/skills/ (project-local), following the Agent Skills specification.

Changes

1. Compatibility table — add Zed row:

Tool	Status
Claude Code	✅ Native · recommended
GitHub Copilot	✅ Supported
Codex	✅ Supported
Cursor	✅ Supported
OpenCode	✅ Supported
Zed	✅ Supported
Gemini	🚧 In progress
Mistral	🚧 In progress

2. Installation section — add Zed to the "Other tools" flat instructions:

Zed — flat

1. Download aidd-framework-zed-flat-<version>.zip.
2. Unzip it into your project root — it materializes .agents/skills/, ready to use.

Note: Zed natively reads CLAUDE.md and AGENTS.md. The flat archive provides AIDD skills via Zed's skill system.

Verification

• Zed reads CLAUDE.md and AGENTS.md natively (confirmed via Zed docs)
• Zed Skill format: SKILL.md with YAML frontmatter in ~/.agents/skills/ or <worktree>/.agents/skills/
• No code changes needed — documentation only