Refresh planner priorities for 4726

[asim]

Summary:

• Drop completed first-agent website wayfinding item after merged PR Gate first-agent quickcheck wayfinding #4725.
• Promote mock provider plan/delegate resume coverage and keep pgx v5 migration next.

Testing:

• git diff --check && go test ./internal/harness/zero-to-hero-ci -run 'TestFirstAgentWayfinding|TestDocs' -count=1
• go test ./... (fails in environment due AtlasCloud live conformance 400 and loopback forbidden grpc tests)
• golangci-lint run ./... (fails because installed golangci-lint was built with Go 1.24 while target is Go 1.25.12)

Closes #4726

[Copilot]

Pull request overview

Updates the autonomous loop’s ranked work queue to reflect the completion of the first-agent website wayfinding work (via PR #4725) and to promote the next highest-value remaining items.

Changes:

• Removes the completed “website first-agent on-ramp” priority item.
• Promotes “mock provider plan-delegate resume scenarios” to the top priority and adjusts its rationale to reference the recently closed gaps.
• Keeps the pgx/v5 migration as the next priority item.

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