Update SpellbookMerge for WotR 2.7 and add zh-CN localization

[WilsonEdwards893]

Summary

• update the mod for the current WotR 2.7 API and Unity Mod Manager metadata
• make all six mythic spellbooks mergeable with base-game caster spellbooks
• discover spellbooks from the preview unit at runtime, so replacement spellbooks from modded archetypes appear as merge choices
• use the current native mythic merge path for caster-level and mythic spell progression instead of overriding ApplySpellbook.Apply with the legacy implementation
• add Simplified Chinese localization and preserve compatibility with external localization packs
• invalidate cached selection items after allowed spellbooks change and avoid direct private-member references

Verification

• compiled against WotR 2.7.0x game assemblies
• verified both embedded configuration resources are present
• audited the output for direct references to non-public Assembly-CSharp types and members
• installed build loads all four custom blueprints and generates 24 static selection items without SpellbookMerge exceptions

The PR is initially marked draft pending one final in-game UI confirmation with a Homebrew Archetypes replacement Wizard spellbook.