Add WowSimsExporter JSON import and upgrade to .NET 10

[harleyj]

Summary

• WowSimsExporter Import: New prominent "Import Gear (WowSimsExporter)" button in the main UI that opens a paste dialog for addon JSON. Imports gear, gems, enchants, race, and talents.
• Auto-detect in existing text box: The existing import/export text box also detects JSON (starts with {) and handles it alongside the existing base64 format.
• Upgraded from .NET 6 to .NET 10: All three projects (RetSim, RetSimDesktop, RetSimWeb) updated.

How It Works

• Parses the WowSimsExporter JSON format (gear.items[] with id, enchant, gems[])
• Maps enchant IDs via EnchantmentID → internal ID reverse lookup
• Assigns gems in socket order, handling both regular and meta gems
• Sets race from the race field (Human, Dwarf, Draenei, BloodElf)
• Parses the talent string (holy-prot-ret format) and sets all 14 configurable talents
• Shows a warning if any items/enchants/gems aren't in RetSim's database

Test plan

• Paste a WowSimsExporter JSON string via the new Import button
• Verify gear, enchants, gems populate correctly on the Gear tab
• Verify race updates on the Settings tab
• Verify talents update on the Settings tab
• Verify the existing base64 import/export still works
• Verify warning dialog appears for items not in the database

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