feat: add release manifest artifact

[Samielakkad]

Summary

• capture pip freeze output in manifest.txt for each upload-charm publication
• upload the manifest with collision-safe artifact names
• migrate manifest and charmcraft-log uploads to the current immutable artifact backend
• keep manifest and log collection independent so one failure cannot suppress the other
• cover generation, upload arguments, unique naming, failure paths, and action integration with focused tests
• rebuild the committed JavaScript action bundles

Closes #20

Validation

• npm test (62 tests passed)
• npm run lint
• npx tsc --noEmit
• npm run build
• focused Prettier check on changed TypeScript files
• Node 24 compatibility check across package engine constraints