chore: rename internal references to fileyard (#79)

Replace fileyard / fileyard with fileyard across docs, manifests,
CI configs, and string references.

- mv apps/cli/fileyard.py -> apps/cli/fileyard.py (entrypoint)
- pyproject.toml [project.scripts] entry name + module path
- All README/docs/AGENTS/manifest.yaml/.env.example references

NOTE: Product/brand string "movi" (e.g. fileyard-mark.svg, fileyard-ci, fileyard-web-api,
FILEYARD_* env vars) is intentionally preserved — that is the product brand,
not the repo name.

Author: xiaojiou176