fix(editor): prevent PIE compile-error modal deadlocks

[Hvizeu]

Problem

When editor.start_pie encounters loaded Blueprints with unresolved compiler errors, Unreal can open a blocking confirmation dialog. Monolith runs in-process, so that modal blocks the game thread and makes the current request and later MCP calls appear deadlocked.

Fix

• Add on_compile_errors to editor.start_pie with two explicit policies.
• refuse is the default: return a structured error containing the offending Blueprint names and paths without starting PIE.
• suppress starts PIE under a narrowly scoped unattended-script guard so Unreal cannot open the blocking confirmation modal.
• Return the selected policy, error count, and Blueprint list on successful starts.
• Reject unknown policies as invalid parameters.
• Document the new request and response contract.
• Add focused automation for invalid policies and structured refusal.

Checklist

• UE 5.7 editor build
• UE 5.8 editor build
• Focused editor automation
• Live refuse and suppress verification
• API reference, module spec, and changelog updated
• Project-agnostic implementation and public description

Validation

• Monolith.Editor.PIE automation passed 2/2.
• Refuse mode returned immediately with structured error data and left MCP responsive.
• Suppress mode started PIE successfully while MCP remained responsive.
• The UE 5.7 and UE 5.8 UnrealEditor targets compiled successfully.
• Full plugin packaging reaches and compiles the changed editor target; a pre-existing MonolithAudioRuntime failure outside this diff still blocks the later packaged-game target.