Add AgentTerm pre-dispatch decision boundary

[mdheller]

Summary

Implements the first concrete tranche for #44: AgentTerm now has a decision-only pre-dispatch boundary object that must exist before later adapters dispatch non-human participants or high-risk actions.

This keeps the SourceOS/SocioProphet lifecycle discipline explicit:

operator / interaction event = evidence input
Agent Registry lookup = identity / session / grant / revocation evidence
Policy Fabric decision = action/context policy evaluation
AgentTerm pre-dispatch decision = local runtime readiness decision
AgentPlane / terminal / Matrix adapter = downstream execution surface
OpsHistory / SourceOSInteractionEvent = record/render path only

Adds

• src/agent_term/pre_dispatch.py
  • AgentTermPreDispatchDecision
  • build_pre_dispatch_decision
  • validate_pre_dispatch_decision
• tests/test_pre_dispatch.py
  • valid resolved non-human participant with grant/session/policy refs;
  • local-config-only non-human participant rejection;
  • revoked grant rejection;
  • side-effecting action without policy refs rejection;
  • sensitive context without policy admission rejection;
  • pre-dispatch record that claims dispatch already happened rejection.
• docs/pre-dispatch-boundary.md

Boundary

This PR does not add live provider calls, terminal execution, Matrix sends, MCP execution, AgentPlane calls, or Agent Registry network access. It only defines and validates the decision object that must exist before those surfaces are wired.

Closes #44.
Advances #8, #18, and #43.