Refresh planner queue after streaming conformance

[asim]

Summary:

• Drop the closed streaming conformance top item after Add A2A streaming conformance harness #4741 shipped it.
• Add Add agent-level x402 spend budget guardrail #4743 as the next builder target: agent-level x402 spend budget guardrail for safe paid tool calls.

Closes #4742

Testing:

• go build ./... was started but manually stopped after it exceeded the planner-doc change budget while compiling dependencies.
• git diff --check passed.

[Copilot]

Pull request overview

Updates the autonomous improvement loop’s ranked work queue to reflect that streaming conformance work has shipped and to point the next automated priority at the x402 spend budget guardrail effort.

Changes:

• Replaces the previous top-ranked “streaming conformance” item with the next target: agent-level x402 spend budget guardrail (#4743).
• Updates the rationale text to reference completion of the streaming conformance work via #4741.

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