MessageProcessor v2 Core Wiring Complete

SystemPrompt hierarchy was standardized, moving toward a pure template renderer. UnifiedSystemMessagePrompt retains placeholders for dynamic context, which will be resolved later in the MessageProcessor flow.

• UnifiedSystemMessagePrompt is now a pure static template renderer without an explicit constructor.

• New format-locked tests enforce lowercase role labels for inputs and title case for Assistant output.

• A compaction pseudo-tool is filtered out during previous messages rendering to prevent duplication.