Remove duplicate scenegraph glyph diagnostic compaction

[chubes4]

Parent: #1076

Problem

ScenegraphNormalizer::compactGlyphCommandBlobDiagnostics() is a dead duplicate of the active implementation owned by ScenegraphDiagnostics. The normalizer method has no callers, while ScenegraphDiagnostics::compact() invokes its own implementation.

Scope

• Remove the unused duplicate from ScenegraphNormalizer.
• Confirm ScenegraphDiagnostics remains the sole owner of glyph diagnostic compaction.
• Add or adjust focused contract coverage only if existing coverage does not prove the active path.

Acceptance criteria

• composer test passes.
• Compacted diagnostic output remains byte-for-byte structurally equivalent for existing fixtures.
• There is one implementation of glyph command blob diagnostic compaction.

AI assistance

OpenAI gpt-5.6-sol via OpenCode identified the dead duplicate and drafted this issue. Chris Huber is responsible for the scope and final changes.