v5: trackers, co-authorship and inference

Spec: SPEC. Build log: PROGRESS. Merged in PR #28.

Research notes: commit co-authorship, issue tracker connections and Microsoft Agent Framework.

• Issue tracker imports from Jira, Linear, GitHub Issues and GitLab Issues, as read-only snapshots.
• Commit co-authorship. Commits, merges and tags carry a Co-authored-by trailer for the accountable person.
• Stack inference and the Analysis phase. A Stack Analyst writes a stack_profile that an Owner approves.
• Shared deployment projects. Parts on one platform form a deployment group.
• PostgreSQL 18 for the product’s own database.