#16674 fix: route PR-media UI tours to GUI minis

PR-media UI tours were routed through the E2E auto fast path, which called simple_pool_picker before the UI-owned resolver. That picker has no test-filter or console-session semantics, so run 36958065338 landed on locked blacksmith-6vcpu-macos-26 despite online GUI minis.

This change keeps UI-filtered auto picks on the UI-aware resolver, selects glaeda-gui-std-xcode-26.6 when configured, and queues on that GUI label when its current capacity is zero instead of falling back to a root or Blacksmith console. Non-UI auto picks keep the shared simple picker.

Validation:

• python3 -m unittest tests.test_ci_pr_runner_pool tests.test_ci_pr_media tests.test_pr_media (354 tests passed)
• Regression coverage proves the UI auto path bypasses simple_pool_picker, prefers an online GUI label, and never chooses root/Blacksmith when GUI capacity is busy or temporarily zero.

The org-level GUI runners on cmux10s and cmux11s were checked read-only. Both retain the glaeda-gui-std-xcode-26.6 registration and current deployment stamp. Their listener gates temporarily withdrew instance 4 during CPU saturation or a held host.lock; at the latest ci-dash snapshot both GUI listeners were online. No restart, relabel, sudo, keychain, or reboot was performed.

— Cobalt g1 🕯️
run: run_cx_bl_ci_meta_20261001_guitour
session: 01c5f8d2-5f42-4d88-9b77-2ac61e1f6d7a

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Summary by cubic

Routes UI PR-media tours through the UI-aware E2E picker so they land on glaeda-gui-std-xcode-26.6 GUI minis instead of the shared simple_pool_picker, which ignores test-filter and console-session semantics.

• Non-UI auto picks still use the simple picker.
• When GUI capacity is zero or a console is locked, the tour queues on the GUI label rather than falling back to a root or Blacksmith console.
• Adds regression tests covering the UI auto path, GUI label preference, and zero-capacity queuing.

Summary by CodeRabbit

• Bug Fixes
  • UI-based test runs now prioritize pools configured for graphical sessions, even when those runners are busy or report no available capacity. This lets runs wait for a compatible runner rather than being routed to a pool that may not support interactive sessions.
  • When no owned pool has machines, runs use the first configured owned pool’s graphical-session label when available; otherwise, the original label is retained.
  • Non-UI runs continue to use the existing automatic pool selection behavior.