Add durable memory facts store and read APIs

[michaelmwu]

Parent: #265

Goal

Add durable memory fact storage and read APIs for user, project, and org facts.

Scope

• Add a memory_facts table or equivalent store.
• Support scopes:
  • user
  • project
  • org
• Store:
  • key
  • structured value
  • visibility
  • source type/ref
  • source excerpt hash
  • created by
  • verification status
  • confidence
  • expiry/review timestamp
  • soft delete timestamp
• Add read helpers/tools:
  • memory_read.get_user_facts
  • memory_read.get_project_facts
  • memory_read.search_context

Design constraint

Prefer authoritative CRM/profile/service fields over inferred memory when both exist.

Acceptance criteria

• Durable facts can be stored with provenance and verification status.
• User/project/org lookups enforce visibility and scope.
• Deleted or expired facts are not returned by default.
• Tests cover read filtering, expiry, soft delete, and authoritative-data precedence.