fix: read actual package version for srt --version output

[javabrett]

Problem

srt --version always returns 1.0.0 regardless of the installed package version.

The current code relies on process.env.npm_package_version:

.version(process.env.npm_package_version || '1.0.0')

npm_package_version is only populated by npm when running package scripts via
npm run or npx. It is not set when executing the compiled binary directly
(e.g. srt --version, srt -c "..."), which is how srt is used in practice.
The hardcoded '1.0.0' fallback is therefore always reached.

Fix

Read the version from package.json at runtime, relative to the compiled
dist/cli.js via import.meta.url:

.version(
  (
    JSON.parse(
      fs.readFileSync(new URL('../package.json', import.meta.url), 'utf-8'),
    ) as { version: string }
  ).version,
)

package.json is always present in an installed npm package, so this is
reliable in all execution contexts. The npm_package_version env var is not
kept as a fallback - when it IS set (npm scripts, npx), the package.json read
returns the same value anyway, making the fallback chain redundant.

Testing

npm run build
node dist/cli.js --version   # now returns the actual version, not 1.0.0