feedback(lang-roc-dev): missing Serialization, Build, and Zero/Default pillars

## Context
- **Task**: Creating `convert-roc-fsharp` skill
- **Used for**: Understanding Roc fundamentals for type mapping and idiom translation

## What Worked Well
- Comprehensive coverage of Module system, Error handling, Concurrency, and Metaprogramming
- Clear platform/application architecture explanation
- Good pattern matching and type system fundamentals
- Excellent testing with expect section

## Suggested Improvements

### 1. Add Serialization Section (Missing Pillar)
The skill mentions Encode/Decode abilities but has no dedicated section explaining:
- [ ] How Encode and Decode abilities work
- [ ] Examples of automatic derivation for records and tag unions
- [ ] Custom encoder/decoder implementations
- [ ] JSON serialization patterns
- [ ] Integration with type providers (if applicable)

**Why important**: Essential for web APIs, file I/O, and interop with other systems

### 2. Add Build & Dependencies Section (Missing Pillar)
Currently no coverage of:
- [ ] `roc build`, `roc run`, `roc test` commands
- [ ] Platform dependency management (platform URLs)
- [ ] How to structure multi-file projects
- [ ] Package/module organization best practices
- [ ] Build configuration options

**Why important**: Developers need to know how to build and structure projects

### 3. Add Zero/Default Values Section (Missing Pillar)
No explicit section on:
- [ ] How Roc handles missing values (tag unions vs other approaches)
- [ ] Default values for types
- [ ] Null-safety patterns beyond Option
- [ ] Zero values and their representations
- [ ] Comparison with other languages' approaches

**Why important**: Critical for understanding nullable types and initialization

## Additional Notes

Current score: **5.5/8 pillars**

These additions would bring lang-roc-dev to **8/8 pillar coverage**, making it a comprehensive foundation skill.

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Feedback from: `/create-lang-conversion-skill roc fsharp`