Add full-stack learning roadmap (EN + UK)

[Rossoline]

What

Adds a full-stack learning roadmap as two new docs — ROADMAP.md and its Ukrainian translation ROADMAP.uk.md.

Why

"TypeScript in a Month" gets a learner through stage 1. This roadmap answers "what next?": a stage-by-stage path from TS basics to shipping a typed full-stack app, so the repo points forward instead of ending at the capstone.

Contents

• Timeline overview table (TypeScript → Node → Express → SQL/MSSQL → Auth → Redis → Docker → React → Next.js) with time estimates and dependencies.
• Recommended order + rationale (backend chain first, then the frontend block).
• Per-stage detail with a concrete project for each stage.
• A final full-stack capstone that ties the stages together, plus study tips.
• English and Ukrainian versions kept in sync.

Notes for the reviewer

• Docs only — no code changes, no changes to any block or exercise.
• The branch is exactly one commit ahead of main (this change only).