feat(security): encrypt game and player names with env-based key

[Adarshkumar0509]

Implements field-level encryption for game.name and player.name as requested in #2232.

Uses Cloak and Cloak.Ecto for AES-256-GCM authenticated encryption. The vault
is configured via the COPI_ENCRYPTION_KEY environment variable in production.
A deterministic test key is configured in test.exs so CI runs without any
additional setup.

The database migration converts the name columns from varchar to binary.
Existing plaintext data is preserved during migration and remains readable
until re-encrypted on next write.

Tested locally with PostgreSQL — 13 tests passing.

Resolved or fixed issue: #2232

###Ai disclosure
Used AI to assist with implementation. The logic, integration with the existing schema and application layer, and all verification were done manually including running migrations and tests locally. No AI-generated noise or unnecessary comments are present in the code. All code are manually written.

[Adarshkumar0509]

@sydseter please check this out ,Happy to make any changes you suggest.

[sydseter]

@Adarshkumar0509 That won't work, we will need to migrate the data and encrypt it in order to be able to load existing player names. Otherwise you get a mismatch between the strings that is saved in the database and the new binary type.

[Adarshkumar0509]

Ok sir I will be working on this