Fix package.json files field (was shipping an empty package)

[markwpearce]

Summary

Found while preparing the first-ever npm/ROPM publish.

Fixed here:

1. "files": ["dist/**/*"] pointed at a directory that has never existed (bsc's outDir is build/, not dist/). npm pack --dry-run confirmed the tarball would contain only LICENSE/README.md/package.json - zero BrighterScript source. Fixed to src/**/*, excluding src/source/roku_modules/** (our own locally-installed copy of rodash, which consumers regenerate for themselves).
2. ropm.rootDir only controls where our own project installs its ropm dependencies (rodash) - it has no effect on how ropm resolves file locations for consumers installing us. That's ropm.packageRootDir, which was missing entirely. Without it, a consumer's ropm install would try to copy from the package root instead of src/.

Verified both fixes with a real end-to-end test: npm pack → install the tarball as a dependency in a scratch project → ropm install → bsc --validate. Files now land correctly under roku_modules, prefixed as expected.

Not fixed here - found via that same test, needs its own investigation before an actual publish:
That end-to-end test surfaced ~1640 real compile errors for the consumer, from issues in the engine source itself, not this config:

• ~676 errors: bare BGE.something self-references inside our own source (called from within the BGE namespace itself) don't get rewritten by ropm's prefixer when it renames the namespace for a consumer
• ~90 errors: ropm's rewriter incorrectly prefixes native Roku SDK types (roTimespan, roBitmap, roAssociativeArray, etc.) in as X type-annotation position, as if they were our own custom types
• 20 errors: our dev environment installs rodash under the friendly alias rodash, but a downstream consumer's transitive install resolves it as tkss_rodash_v0 (derived from the real npm name @tkss/rodash), so our bundled code's bare rodash.xxx() calls don't resolve for anyone but us

None of the existing examples would ever catch this, since they consume the engine via a direct file-copy trick in bsconfig.json, never through real ropm install. Publishing is on hold until that's addressed.

Test plan

• npm run validate / npm run lint pass
• npm pack --dry-run includes all engine source, excludes roku_modules
• Real ropm-consumer test confirms files now install to the right location, correctly prefixed
• This PR's own validate check passes