Remove unused generated artifacts

[Finesssee]

Summary

• Delete checked-in generated Tauri schema JSON artifacts and ignore regenerated schema outputs
• Remove the one-use directories dependency in favor of already-used dirs
• Inline the one-call prerequisite help helper in dev.ps1

Validation

• cargo fmt --all for both Rust manifests
• cargo test --manifest-path apps\desktop-tauri\src-tauri\Cargo.toml (247 passed)
• cargo clippy --manifest-path rust\Cargo.toml --all-targets -- -D warnings
• cargo clippy --manifest-path apps\desktop-tauri\src-tauri\Cargo.toml --all-targets -- -D warnings
• cargo test --manifest-path rust\Cargo.toml (425 passed)
• pnpm --dir apps\desktop-tauri run build
• PowerShell parser check for dev.ps1
• git diff --check

GitHub Actions are currently blocked by the repository/account billing lock, so this uses local CI-equivalent validation.