Delegate droste code to the installed Droste Code executable

[shanev]

Objective

Once Droste Code clears its efficacy and release gates, make droste code a thin process-level alias for the separately installed droste-code executable. Core Droste must not import or depend on the Droste Code package.

Tracking: tensor-systems/droste-code#12

Acceptance criteria

• Implementation is gated on the Droste Code M1 evaluation and v0.1 packaging work.
• Resolve droste-code from PATH and delegate argv without importing the package.
• Preserve the child exit status and normal signal behavior.
• If the executable is absent, print an actionable installation message.
• Existing naked droste behavior and authentication commands remain unchanged.
• Cover argv forwarding, missing executable, exit status, and signal behavior with tests.
• Document the alias and the fact that Droste Code is installed/versioned separately.
• Do not add a core dependency on droste-code.

Why process delegation

The Python proof of concept can iterate with Droste directly, while a later Rust or TypeScript shell can remain independent. A process boundary keeps the core CLI stable and prevents either package from constraining the other runtime.