Restructure portmgr's scattered policy documents into a coherent
policies/ subdirectory with clear hierarchy:
- _index.adoc: Hub page linking all policy documents
- integrity.adoc: Collection integrity and regression testing
- committing.adoc: When commits are allowed (open/frozen/thawed)
- contributors.adoc: Maintainer and committer timeouts
- eol.adoc: Supported release and branch policy
- qa.adoc: Quality assurance activities
Content consolidated from previous policies.adoc, policies_*.adoc,
implementation.adoc, and qa.adoc files. No policy changes; this is
purely organizational for improved discoverability.
Update portmgr/_index.adoc to link to new structure.
Co-Authored-By: Claude Haiku 4.5 <noreply@anthropic.com>