Add read-only Gira work-map import from workspace status JSON

[StatPan]

Goal

Add a read-only Agentree import path for Gira workspace queue/status JSON so Agentree can render a live work map without owning the canonical work state.

Parent context: #15, #17
Related Gira: StatPan/gira#684, StatPan/gira#685

Context

Agentree should be the live visual supervision and run/evidence correlation layer. Gira remains the GitHub-native work contract and export source. The next useful Agentree slice is a read-only import of Gira/GitHub work identity into Agentree work nodes.

Scope

• Inspect current Agentree work-node schema and Gira/GitHub identity mapping work.
• Define or implement a read-only import adapter for Gira workspace queue/status JSON.
• Map repo, issue, PR, branch, status, checks, review state, and next action into Agentree nodes/edges.
• Preserve unknown/low-confidence attribution rather than inventing ownership.

Acceptance Criteria

• Agentree can consume a sample Gira workspace/status JSON export or the design defines the exact schema gap blocking it.
• Work nodes preserve Gira/GitHub identity and source links.
• The implementation or design remains read-only and does not update GitHub/Gira state.
• No hosted runtime, credential write, or worker execution engine is added.

Boundaries

• Do not make Agentree a second project tracker.
• Do not infer private productivity metrics.
• Do not mutate GitHub issues/PRs from Agentree in this slice.