docs: add public roadmap with feature voting (#4)

[Alexsantossp71]

Summary

Adds a public ROADMAP.md inspired by the discussion in #4 (Roadmap & Feature Voting).

What this PR does

• Creates a structured roadmap organized by category (Near-term, Skills, Docs & DX)
• Uses clear tables with feature descriptions and status tracking
• Includes a "How to Vote" section encouraging community engagement via GitHub reactions
• Links back to issue 🗺️ Roadmap & Feature Voting #4 and to good first issue labels for new contributors

Motivation

The project currently has a pinned issue (#4) serving as the roadmap, but a dedicated ROADMAP.md file:

• Is more discoverable (appears in the repo file tree)
• Can be referenced from the README
• Provides a stable, version-controlled planning document
• Makes it easier for new contributors to find what to work on

Closes #4