[FEATURE] Add private Dedicated agent topology (K9)

[EItanya]

Summary

Implement K9 Dedicated AgentTemplate bindings as private, parent-owned multi-Actor topology.

Unlike public K11 delegation, a Dedicated child is provisioned as part of its parent AgentInstance and is not independently addressable by users.

Prerequisites

• Single-member lifecycle and conformance coverage are stable.
• K11 provides the reusable A2A invocation, streaming, cancellation, credential, and lineage machinery.

Scope

• Compile a runtime bundle and immutable backing version for every Dedicated boundary.
• Provision every member through the existing AgentInstance workflow.
• Give each binding a private A2A endpoint and credentials scoped to that binding and child.
• Expose the child through the harness's native tool mechanism, using MCP-to-A2A only where native A2A invocation is unavailable.
• Stream child progress and cancellation through the parent task and return terminal output as the tool result.
• Keep Actor identity, credentials, and target selection private.
• Persist binding and conversation handles in snapshot-covered durable storage.
• Apply lifecycle and deletion atomically from the caller's perspective across all members.
• Extend checkpoint and fork consistently across all members.
• Add partial-failure, retry, cancellation, lifecycle, checkpoint, and fork E2E coverage.

Out of scope

• Public invocation between independently created AgentInstances; that belongs to K11.
• Child input_required continuation until its user-facing semantics are designed.

Completion criteria

• Creating a parent deterministically creates its Dedicated members or safely resumes/cleans up partial work.
• Dedicated children have no public AgentInstance routing authority.
• Parent lifecycle, deletion, checkpoint, and fork cannot leave an untracked child Actor.
• Child event streaming and cancellation work through the parent task.

Roadmap: docs/plans/api-v2-execution-plan.md, K9.