Add a shared filament library used by auto-paint profiles

Kromacut could move toward a shared filament library instead of keeping filaments only inside individual auto-paint profiles.

Today, profiles behave like self-contained filament sets. A more flexible model would let users save filaments once, then build multiple profiles that reference those saved filaments.

Example model:

• A filament library contains reusable filament entries.
• A profile contains references to multiple filaments from that library.
• Multiple profiles can reference the same filament.
• Updating a shared filament could optionally affect every profile that uses it, depending on the final UX design.

Why this matters:
Users may reuse the same real spools across many auto-paint profiles. Duplicating filament data across profiles makes it easier for names, colors, TD values, or calibration data to drift out of sync. A shared library would make filament management feel more like managing actual materials.

Areas that need planning:

• UI for managing the global filament list.
• UI for adding/removing library filaments from a profile.
• How profiles display referenced filaments.
• How edits to a shared filament affect existing profiles.
• How to handle copying/forking a filament for one profile only.
• Migration from existing saved profiles.
• Import/export behavior for profiles and filament libraries.
• Backward compatibility with existing .kapp / .kfil / JSON files.
• How this interacts with calibration data and future project files.

Desired outcome:
Users can maintain one reusable list of filaments and assemble profiles from that list, instead of duplicating the same filament data across multiple profiles.

The issue names no files, tests, or entry points. Start by mapping where profiles and filament data are stored, edited, imported, and exported, then document the migration and sharing behavior before implementation. Done means reusable library filaments can be referenced by multiple profiles without breaking existing files.