feat(cli): Make skore agent-friendly

[Aljutor]

Why

Make the CLI work naturally for both people and coding agents, while keeping agent metadata in one place.

What changed

• Detect Claude Code, Cursor, Gemini CLI, Codex CLI, Pi, and OpenCode from their environment variables.
• Use plain, non-interactive output when running inside an agent, CI, or a non-TTY environment.
• Show an agent-specific quick start and automatically select the appropriate skills directory.
• Automatically select supported harnesses.
• Avoid launching a nested agent when already running inside that harness.
• Keep the existing interactive TUIs for people using the CLI directly.
• Consolidate detection, skill paths, and harness behavior into one Agent registry.
• Preserve existing public values such as --agent claude-code, --harness claude, and legacy .skore configurations.
• Simplify skills discovery by showing the catalog from skills install in non-interactive mode and removing the redundant skills find command.

Verification

• 203 tests pass.
• All pre-commit hooks pass, including Ruff, formatting, typos, and mypy.