fix(cli): detect Deno JSR cli entrypoint

[rohan-patnaik]

Fixes #1383.

What changed

isMain() now recognizes Deno JSR executions where the main module is reported as jsr:@webpod/zx, jsr:@webpod/zx/., or jsr:@webpod/zx/cli.

This keeps the existing Node/file-url behavior unchanged, but lets the CLI autorun when zx is launched through its JSR entrypoint.

Why

When running through JSR, Deno does not always expose the CLI as a local file path. The old isMain() check only handled local file URLs or import.meta.main, so deno run jsr:@webpod/zx could import the module without entering the CLI path.

Usage demo

import { isMain } from 'zx/cli'

// Simulates Deno reporting the JSR package root as the main module.
globalThis.Deno = { mainModule: 'jsr:@webpod/zx' }
console.log(isMain('jsr:@webpod/zx/cli')) // true

• Setup Set the latest Node.js LTS version.
• Build: I’ve run npm build before committing and verified the bundle updates correctly.
• Tests: I’ve run focused tests and size checks. Added regression coverage for the JSR main-module cases.
• Docs: Not needed; this is a CLI entrypoint fix covered by tests.
• Sign Commits have verified signatures and follow conventional commits spec.
• CoC: My changes follow the project’s coding guidelines and Code of Conduct.
• Review: This PR represents original work and is not solely generated by AI tools.