Add memory fragment collection & UI

[MarcPladellorensPerez]

Implements collectible memory fragments: adds fragment_id map property and reads it when spawning MemoryFragment entities. MemoryFragment notifies Player on collect; Player gains arrays to track collected/new fragments. SaveSystem persists hasMemoryFragment[0..2] to XML and restores them (new flags cleared on load). Scene: stores fragment persistence across map loads, loads/unloads collected variant textures, draws collected/new animations in the inventory, shows fragment markers on the minimap, and preserves fragment state during submap loads/unloads. Minor UI tweak (inventory portrait vertical offset) and initialization of timers/texture pointers included. MapTemplate.tmx updated with a default fragment_id property.

Canvis

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Tipus de canvi

• feat: Nova funcionalitat
• fix: Correcció de bug
• art: Asset gràfic
• docs: Documentació
• refactor: Refactorització de codi
• build: Canvis al sistema de build

Checklist

• El codi compila sense errors
• He provat els canvis localment
• He seguit les naming conventions (PascalCase classes, camelCase mètodes, m_ membres)
• He usat Conventional Commits al títol del PR
• He enllaçat la Issue corresponent