Improve README presentation

[shaypal5]

Summary

• Rework the root README into a clearer first-visit gateway for hletterscriptgen.
• Add CI/license/Python/schema badges and a visual output-contract diagram.
• Clarify repo ownership boundaries, HeOCR pipeline position, CLI usage, and the letter_set.v1 output contract.
• Update docs/README.md with the required creator credits and remove stale wording that said the generation pipeline was not implemented.
• Add the required creator attribution near the top and bottom of each README file.
• Update repository metadata description and topics to match the project purpose.

Validation

• python -m ruff check .
• python -m mypy
• python -m pytest
• PYTHONPATH=src python -m hletterscriptgen validate examples/letter_set/writer_example.json
• PYTHONPATH=src python -m hletterscriptgen schema --format json
• README smoke check for exactly two creator mentions in each README
• git diff --check

Milestone

No milestone assigned. The repository has roadmap milestones for implementation stages, but this PR is documentation/presentability work and does not map cleanly to a specific implementation milestone.