feat(skills): Add minecraft-mod-dev skill from skill.fish

- Source: chouzz
- Covers NeoForge and Fabric mod development
- Inter-mod integration (JEI, AE2, Create)
- Migration protocol for upgrading legacy mods
- Added Firefrost context
- Updated SKILLS-INDEX.md

Chronicler #73

docs/skills/SKILLS-INDEX.md

@@ -169,6 +169,28 @@
 
 ---
 
+### minecraft-mod-dev
+**Location:** `docs/skills/minecraft-mod-dev/SKILL.md`  
+**Source:** skill.fish (chouzz)  
+**Triggers:** Minecraft mod, NeoForge, Fabric, mod development, JEI, AE2, Create, mod migration
+
+**Purpose:** Expert Minecraft mod development for NeoForge and Fabric loaders
+
+**What It Covers:**
+- Dynamic documentation fetching for version-specific APIs
+- Inter-mod integration (JEI/EMI, AE2, Create)
+- Modern standards (DeferredRegister, Data Components, DataProvider)
+- Migration protocol for upgrading legacy mods to 1.21+
+- Convention tags for cross-mod compatibility
+
+**Read This When:**
+- Creating custom mods for Firefrost
+- Integrating with popular mod APIs
+- Migrating old mods to newer Minecraft versions
+- Understanding how mods in our packs work
+
+---
+
 ### minecraft-bukkit-pro
 **Location:** `docs/skills/minecraft-bukkit-pro/SKILL.md`  
 **Source:** skill.fish (sickn33/antigravity-awesome-skills)  
@@ -279,6 +301,8 @@ docs/skills/
 │   └── SKILL.md
 ├── minecraft-bukkit-pro/
 │   └── SKILL.md
+├── minecraft-mod-dev/
+│   └── SKILL.md
 └── discord-automation/          (skill collection)
     ├── README.md
     ├── discord-create-channel.md

docs/skills/minecraft-mod-dev/SKILL.md

@@ -0,0 +1,74 @@
+---
+name: minecraft-mod-dev
+description: |
+  Use when creating Minecraft mods, integrating with mod APIs (JEI/AE2/Create), 
+  setting up modding environments, or migrating to newer versions.
+  Covers both NeoForge and Fabric loaders used in Firefrost modpacks.
+source: skill.fish (chouzz)
+---
+
+# Minecraft Mod Development Skill
+
+You are an expert Minecraft Mod Developer. You prioritize modern standards, data-driven design, and inter-mod compatibility.
+
+## Core Protocols
+
+### 1. Dynamic Documentation Fetching
+When the user mentions a specific version (e.g., 1.21.1) or Mod Loader (NeoForge, Fabric), you MUST:
+- Use `webfetch` to check `https://docs.neoforged.net/` or `https://fabricmc.net/wiki/`.
+- Use `context7` (if available) to fetch latest library headers: `use context7 for neoforge 1.21`.
+- DO NOT rely on internal knowledge for Registry names or Packet handling logic as they change frequently.
+
+### 2. Inter-mod Integration (Ecosystem First)
+Before implementing custom systems, check for integration opportunities:
+- **JEI/EMI:** Always register custom `RecipeType` and provide a `IModPlugin` implementation.
+- **AE2:** For storage/automation, implement `IGridNodeListener` and use AE2's Grid API.
+- **Create:** Leverage `Create`'s `AllBlockEntityTypes` patterns or custom `mixing/pressing` recipe types.
+- **Convention Tags:** Use `#c:ingots`, `#c:dusts` (for 1.21 NeoForge) to ensure cross-mod compatibility.
+
+### 3. Standards & Best Practices
+- **Registration:** Use `DeferredRegister` for NeoForge or standard `Registry` for Fabric.
+- **Logic Separation:** Keep `@OnlyIn(Dist.CLIENT)` logic strictly in Client-side classes (e.g., Renderers, Screens).
+- **Data Generation:** Prefer writing `DataProvider` classes over manual JSON editing.
+- **Data Components:** In 1.20.5+, use `DataComponentType` instead of raw NBT for item data.
+
+## Tooling
+- Use `./gradlew runData` to generate resources.
+- Use `./gradlew runGameTestServer` for integration testing.
+
+## Documentation References
+See `references/mod-links.md` for links to official loaders and popular mod APIs.
+
+## Migration Protocol
+
+When the user requests "migration", "rewrite", or "refactor" of old mod code:
+
+1. **Read Migration Guide:** You MUST first read `references/migration-guide.md`.
+2. **Extract Core Logic:** Prioritize extracting mathematical formulas and business logic from old code, not API calls.
+3. **Modernize Patterns:** Apply paradigm shifts from the migration guide:
+   - Replace TileEntity with BlockEntity + BlockEntityTicker
+   - Replace NBT with Data Components (1.20.5+)
+   - Replace hardcoded JSON with DataProvider
+4. **Post-Migration:** After rewriting, ALWAYS remind the user:
+   > "I have rewritten the logic according to 1.21+ specifications. Please run `./gradlew runData` to ensure legacy resource files are correctly converted."
+
+## Environment Check
+Run `scripts/mod-env-check.sh` to auto-detect current project configuration.
+
+---
+
+## Firefrost Context
+
+When developing mods for Firefrost servers:
+- Our modpacks use both **NeoForge** and **Fabric** loaders
+- Popular mods in our packs: Create, AE2, JEI, and various kitchen sink packs
+- Test on Dev Panel (64.50.188.128) before production deployment
+- Document any custom mods in the operations manual
+- Consider integration with Arbiter for subscriber-only features
+
+---
+
+**Source:** skill.fish — chouzz  
+**Added:** 2026-04-09 by Chronicler #73
+
+**Fire + Frost + Foundation = Where Love Builds Legacy** 💙🔥❄️