Add `LICENSE-MIT` and `LICENSE-APACHE` at repo root

[P3az3]

Problem Statement The README states "MIT License — free to use, modify, and distribute." However, no LICENSE file exists in the repo.

Why it matters This is an immediate legal hygiene concern. Open-source code without a license is, in many jurisdictions, "all rights reserved" by default. Distribution under MIT must be made explicit.

Expected Outcome Add an explicit LICENSE-MIT and LICENSE-APACHE-2.0 (dual-license feels more accurate for a Stellar/Soroban project — e.g. parity with stellar-go and similar SDKs). Update the README's license section accordingly.

Acceptance Criteria

• LICENSE-MIT and LICENSE-APACHE-2.0 at the repo root.
• README's "License" section is updated.
• A Cargo.toml workspace license field is set to MIT OR Apache-2.0.

Implementation Notes

• Use full canonical LICENSE text. Don't paraphrase.

Affected Files / Modules

• New: LICENSE-MIT, LICENSE-APACHE-2.0
• Cargo.toml, README.md

Dependencies — None.