fix(cli): error clearly when no main package is present

[Pragati5-DEBUG]

Summary

Detect when the current directory has no main package before vodka / vodka run dev builds and runs
Exit with a clear error instead of writing a non-executable tmp/vodka-build.exe that Windows rejects with “This version of %1 is not compatible…”

Why

Running the CLI inside the framework repo (a library, not an app) made go build -o … . produce an archive named .exe. Trying to execute it failed with a confusing OS error.

Test plan

In the framework repo: vodka prints the new message and exits with code 1

In a project from vodka create: vodka still builds and runs

vodka run dev in a fullstack app still starts Vite + backend

After the fix

[vercel]

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