GUI: Fix PR3184 bugs (icon distortion, memory leak, nickname refresh) and optimize cache

[jolavillette]

Summary of improvements and fixes for PR RetroShare#3184

Following a technical review and feedback regarding UI and memory management, several improvements have been implemented:

🎨 UI & Visual Fixes

• Fix Icon Distortion: Corrected the scaling logic in [makeColoredGroupIcon]. Icons are now centered proportionally instead of being stretched to fit the square frame.
• Unified Aesthetics: Harmonized HSL parameters (Saturation/Lightness) across all generated group and circle icons for a consistent pastel look.
• Dynamic Nickname Update: Fixed the issue where nicknames and icons in the "Circles" list wouldn't refresh when updated. They are now correctly reloaded during GXS events.

🐛 Stability & Memory

• Fix Potential Memory Leak: Replaced raw pointer allocations with std::shared_ptr in IdDialog::updateCircles() to ensure memory is safely released even if the dialog is closed during asynchronous processing.
• Thread Safety: Verified and maintained proper mutex locking for all cache and pending data operations.

⚡ Performance & Optimization

• RAM Efficiency: Reduced the default size of circle icons in the cache from ORIGINAL (192px) to MEDIUM (96px). This significantly reduces RAM usage while maintaining perfect visual quality for list displays.
• Cache Integrity: Added a separator | in cache keys to prevent theoretical collisions between different ID/Path combinations.
• Code Cleanup: Removed obsolete commented-out blocks in [IdDialog.cpp].