Add Java learning roadmap README

[Copilot]

Student is ~5 days into Java with no existing README or learning plan. Adds a structured, no-emoji roadmap tailored to a Level 4 cybersecurity-pathway undergraduate.

Skill baseline (derived from existing projects)

• Basic OOP: multiple classes, constructors, instance vs static members
• Control flow, loops, method overloading, type casting
• Standard library: Scanner, Random, Math, StringBuilder, LocalDate
• Exception handling, Thread.sleep, menu-driven CLI patterns

Roadmap structure (6 phases, ~3 months)

• Phase 1-2 (Weeks 1-4): Projects using only known concepts (number guessing, calculator, grade tracker), then ArrayList-based OOP (contact book, bank account, student records)
• Phase 3 (Weeks 5-6): File I/O — FileWriter/BufferedReader, timestamped logging, notes app, Caesar cipher with file output
• Phase 4 (Weeks 7-9): Cybersecurity-relevant — hashing tool (MessageDigest / SHA-256), brute force timer, cipher breaker
• Phase 5 (Weeks 10-12): Intermediate OOP — inheritance, interfaces, polymorphism, HashMap, Vigenère cipher
• Phase 6 (Months 3-4): Networking and concurrency — TCP port scanner, multithreaded scanner, HTTP client

Phases 3-6 each include Core Concepts, Resources, and Knowledge Required sections. Port scanner phase includes a legal disclaimer regarding unauthorised scanning.

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