Add FunctionalVerificationRunService

What does this MR do and why?

• Adds Ai::DuoAgentPlatform::FunctionalVerificationRunService for reading and mutating the current functional verification run for a check type
• Adds Ai::DuoAgentPlatformFunctionVerificationCheck module with agentic_chat_verification_check_enabled? method to check availability for GQL entry points and FE.

References

Closes #618769 (closed)

How to set up and validate locally

In the Rails console:

service = Ai::DuoAgentPlatform::FunctionalVerificationRunService.new(check_type: :agentic_chat)

# 1. nothing run yet
p service.read # => { state: "not_run" }

# 2. start a run
service.mark_running(workflow_id: 1)
p service.read # => { state: "running", workflow_id: 1, ... }

# 3. complete it (pass)
service.mark_completed(workflow_id: 1, status: :passed)
p service.read # => { state: "passed", ... }

# 4. start a new run, let it go stale, confirm read self-heals it to failed
service.mark_running(workflow_id: 2)
Ai::DuoAgentPlatform::FunctionalVerificationRun.current_for(:agentic_chat)
  .update_column(:updated_at, 200.seconds.ago) # simulate stale
p service.read # => { state: "failed", message: "Verification check timed out." }

# 5. race guard: mark_completed on a stale run after timeout already fired should be a no-op
result = Ai::DuoAgentPlatform::FunctionalVerificationRun.complete_run(
  check_type: :agentic_chat, workflow_id: 2, status: :passed, message: nil
)
p result # => false, since status is no longer :running... wait check scope

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