🧹 Refactor executeMediaOp for improved maintainability

[MarsLuay]

🎯 What: Extracted the operations inside the large switch statement in executeMediaOp within src/ai/pptxOpExecutor.ts into five separate handler functions (handleSetImageCrop, handleFitImageToFrame, handleResetImage, handleReplaceImage, handleReplaceImageFromShape).
💡 Why: This drastically improves readability and maintainability by keeping function size small and separating the distinct logic flows of different pptx media operations.
✅ Verification: Verified locally with npm run typecheck, npm run lint, and tests.
✨ Result: A more modular and cleaner approach for PPTX media operations.

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PR created automatically by Jules for task 16180148752415539239 started by @MarsLuay

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