Detect more Unity license-contention signatures and cover the device-build job

[allister-beamable]

Follow-up to #4702. The serial-throttling (max-parallel: 1) is the real fix and should keep these gates from tripping — this PR just makes the detection solid for the cases where they do.

#4702 added a problem matcher plus a post-failure annotation to the two Unity test shards, but left two gaps:

1. The matcher missed the leading contention signature

It recognized only No valid Unity Editor license found and the ULF-return tail. The actual leading symptom of a lost seat is the licensing subsystem's Found 0 entitlement groups and 0 free entitlements 404, preceded by Access token is unavailable; failed to update. That 404 (plus the downstream com.unity.editor.headless was not found) is what headlined the contention failures, yet none of it matched — so the live annotations never named the real cause.

This adds two matcher patterns: unity-license-no-entitlements and unity-license-access-token-unavailable.

2. The device-build job had no detection at all

Build for {iOS,Android,StandaloneWindows,StandaloneOSX} shares the UNITY_SERIAL_DEVOPS seat and is exactly where contention surfaced, but it had neither the matcher registration nor an annotation step — only the test shards did.

This registers the matcher in the build job and adds an annotation step. The build job keys off an empty dist/ (a seat failure aborts before the player is built). Because an empty dist/ also describes a genuine build break, that message points back at the license annotations rather than asserting contention outright — unlike the test shards' XML check.

Notes

• Problem-matcher annotations are informational; they do not change job outcome (still controlled by step exit codes), so a stray match can't turn a green build red.
• Container-action stdout scope for the matcher is still unconfirmed (same caveat Throttle Unity CI license activations to the per-serial seat budget #4702 carries); the artifact-absence annotation is the reliable fallback either way.

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