Use dprint as the default formatter

[SandroMaglione]

Summary

• replace Prettier with dprint and use the same pinned formatter configuration as Effect
• add the local dprint dependency and update the formatting scripts
• configure VS Code/Cursor to use the workspace dprint executable on save
• recommend the dprint editor extension and normalize the existing supported files
• make incomplete README TypeScript fragments formatter-stable

Root cause

The repository did not provide a local dprint executable, root configuration, or workspace editor path on the current main branch. The editor extension therefore fell back to a globally installed dprint, which was unavailable, and reported that no configuration file could be found.

Impact

Contributors can run formatting through pnpm or save supported files in VS Code/Cursor and receive the same output as the Effect repository without installing dprint globally.

Validation

• dprint check
• tsc -p tsconfig.json --noEmit
• tsc -p tsconfig.build.json
• vitest run — 207 tests passed across 5 files
• confirmed dprint.json is byte-identical to references/effect/dprint.json