docs: simplify setup and client compatibility

[zelentsov-dev]

Summary

• replace the credential-heavy first run with a five-step Quick Start
• document the real macOS-only server boundary separately from cross-platform MCP clients
• update Codex, Claude, Gemini, VS Code, Continue, Cursor, and Devin Desktop setup
• add safer credential storage, verification commands, troubleshooting, and support guidance

Verification

• GitHub GFM render succeeded with all details sections balanced
• all README JSON and TOML examples parse successfully
• official documentation links return successfully
• Codex and Claude CLI syntax checked against installed command help
• installed asc-mcp version command verified
• documentation-only change; no Swift build or test run