Replace fp-ts with plain TypeScript

[mkobayashime]

Summary

• Replaced all fp-ts usage with native TypeScript features to reduce dependency complexity
• Removed fp-ts package from devDependencies

Changes

• Option<FileProperties> → FileProperties | null
• O.none/O.some() → null/direct object return
• pipe() function composition → direct Promise.all() with .flatMap()
• A.compact → .filter() with type guard
• A.sort() with Ord → native .sort() with localeCompare()
• O.isSome() → simple null checks

Test plan

• All tests pass (16/16)
• TypeScript compilation succeeds
• Doc generation script works correctly
• Manifest generation works correctly