Add a Caesar cipher encode/decode script

[utk2103]

Add a Caesar cipher encode/decode script to scripts/.

Why

Smallest possible introduction to string manipulation, modular arithmetic, and the idea of a reversible transformation. Also a nice lead-in to "why this is not real encryption".

Suggested file

scripts/caesar_cipher.py

What it should do

• python scripts/caesar_cipher.py encode "hello world" --shift 3
• python scripts/caesar_cipher.py decode "khoor zruog" --shift 3
• Bonus: --brute-force on decode, printing all 25 candidate shifts.

Acceptance criteria

• Preserves case, and leaves spaces/digits/punctuation untouched.
• Decoding an encoded message returns the exact original string.
• One assert-based self-check under if __name__ == "__main__": or a tiny test_caesar_cipher.py proving the round-trip.
• A comment noting this is a learning exercise, not secure encryption.

Inspiration

caesar_cipher from Awesome-Python-Scripts.

Good first issue — comment below to get assigned.