docs: license and secure public access

[MaharshPatelX]

Summary

• add the canonical Apache License 2.0 for original project code and documentation
• document the owner-maintained, collaborator-only contribution model
• define the GitHub access controls and security automation required for public release
• preserve separate licensing boundaries for xRouteBench, Liquid AI models, and other upstream artifacts

Validation

• LICENSE matches the Apache Software Foundation's canonical LICENSE-2.0 text
• git diff --check passes
• local Python checks were unavailable because no Python runtime is installed on this machine; GitHub CI must pass on Python 3.11 and 3.12 before merge

Publication sequence

The repository remains private during review. After this PR passes CI and merges, repository visibility will change to public and the documented collaborator-only, branch-protection, and security-scanning settings will be applied and verified.