feat(cli): derive generate-worker arguments from package.json like generate-shim

[toiroakr]

Background

politty generate-shim (#633) derives its arguments from package.json: the output path from the bin paths, the program name from the bin names, and the entry from conventional built modules. Its sibling build-time command politty generate-worker still requires --bin and --program to be passed explicitly, so the two commands now have different setup ergonomics.

Proposal

Bring generate-worker in line with generate-shim:

• --program: default to the first bin name in the nearest package.json (falling back to the package name without its scope).
• --bin: default to the first bin path (the built entry the worker should invoke — note that once a compile-cache shim is in place, bin points at the shim, which is also a valid target).
• --shell: consider allowing repeats or an all value so one invocation can generate bash/zsh/fish workers in a single postbuild script.

Notes

• Both commands are optional build-time optimizations, so this is purely an ergonomics change; explicit flags keep working.
• Raised while reviewing perf: enable Node.js on-disk compile cache for faster warm starts #633 (generate-shim); intentionally left out of that PR's scope.