fix(cli): require explicit init for guidance

[neusse]

Summary

• remove the silent guidance installer from normal piped MCP startup
• keep --client accepted and validated for command compatibility
• document that guidance installation requires an explicit konnect init
• regression-test clean-home and install/uninstall/start sequences for both Claude and Codex with the real CLI process

Closes #242.

Root cause and design

Server startup treated an absent .installed-{client} marker as a first launch and called the silent installer. uninstall deliberately removes that same marker, so the next MCP launch could not distinguish an explicit uninstall from a new installation and recreated the guidance.

This selects the simpler policy approved in #242: server startup performs no guidance installation at all. Installation remains available only through the explicit konnect init [--client ...] command. No tombstone or new persistent state is needed.

Compatibility and migration

• --client claude and --client codex remain valid server arguments.
• Existing explicit init, status, and uninstall behavior is unchanged.
• TTY/double-click setup behavior is unchanged.
• A fresh MCP registration no longer installs guidance implicitly; users who want bundled guidance run konnect init once.

Tests

• cargo test --workspace --locked --lib --tests
• cargo test --workspace --locked --doc
• cargo clippy --workspace --locked --all-targets -- -D warnings
• cargo fmt --all -- --check
• python -m unittest discover -s plugin/tests -v (KiCad 10 bundled Python)

The real-process home-directory regression runs on Linux and macOS. It is intentionally excluded on Windows because dirs::home_dir() uses SHGetKnownFolderPath there and ignores HOME/USERPROFILE; attempting to redirect it would risk the runner's real client configuration. The normal Windows unit/integration suite remains green. Live-KiCad tests retain their repository-defined ignored status.

Risk and rollback

Risk is limited to removing an implicit side effect. Rollback is the single commit, but would restore the destructive post-uninstall behavior. No file format, IPC protocol, packaging, schema, or configuration-key changes are involved.