Utils: implement gatherDebugInfo() for runtime diagnostics

[N0153128]

There is no way to gather a snapshot of full runtime state for debugging. Debug info is currently scattered across ProcessingContext, plugin config, and global config with no unified view.

Requested change

Add Utils.gatherDebugInfo() that collects on demand:

public static String gatherDebugInfo(
        ProcessingContext context,
        MediaPlugin plugin,
        MediaConfig config,
        GlobalConfig globalConfig)

• File identity from ProcessingContext
• Plugin name/version from MediaConfig
• Output path, size limits from GlobalConfig
• Plugin-specific values via MediaConfig.get()
• Returns a formatted human-readable key/value String

Add a Path overload that writes the output as .txt to the output directory.

Acceptance criteria

• gatherDebugInfo() implemented with String return
• gatherDebugInfo(Path outputPath) overload saves as .txt
• Output covers all four input sources