Add dependency-light TUI snapshot scaffold

[mdheller]

Summary

Adds a dependency-light operator snapshot model for AgentTerm.

This PR implements the first tested TUI model layer for issue #9 without requiring live Textual rendering or a Matrix homeserver in CI.

It adds:

• tui_model.py with panes, lines, snapshots, classification, risk-state/status mapping, and text rendering.
• agent-term-snapshot console script for rendering an operator snapshot from the local SQLite event log.
• Tests for pane classification, visible operator risk states, room/thread extraction, domain-pane routing, and text rendering.

Boundary decisions

• This is a view-model/render scaffold, not the final Textual application.
• It does not bypass Matrix, Agent Registry, Policy Fabric, cloudshell-fog, AgentPlane, or any SourceOS authority plane.
• It makes denied, pending, revoked, blocked, and active states visible in the terminal surface.
• It creates the stable model a future Textual UI can render without coupling the UI to live SDKs.

Validation

Expected CI:

ruff check .
pytest

Part of #9.