docs: add missing organization governance defaults

[ORESoftware]

What changed

Adds only baseline organization-governance files that were absent on the latest default branch. All existing documentation remains byte-for-byte untouched.

Added paths

• PULL_REQUEST_TEMPLATE.md

Validation

• generated from the reviewed portfolio baseline;
• credential-shaped content scan passed;
• repository identity, public visibility, and owner authorization were verified;
• post-merge verification requires all 15 baseline paths on main.

[linear-code]

DEN-2432