feedback(meta-convert-dev): from convert-scala-elixir creation

## Feedback: meta-convert-dev

### Context
- **Task**: Creating `convert-scala-elixir` skill
- **Used for**: Foundation patterns, APTV workflow, type mapping strategies

### What Worked Well
- APTV (Analyze → Plan → Transform → Validate) workflow provided clear structure for organizing the conversion skill
- Type mapping table templates were excellent references for creating comprehensive type system mappings
- Idiom translation patterns helped structure the "Why this translation" explanations
- Examples of existing conversion skills (convert-erlang-elixir, convert-typescript-rust) were invaluable for understanding depth and quality expectations
- The "This Skill Extends" / "This Skill Adds" / "This Skill Does NOT Cover" structure provides clear boundaries

### Suggested Improvements
- [ ] Add more guidance on **platform ecosystem differences** (JVM vs BEAM vs Native vs Scripting)
- The template mentions memory models but could expand on runtime platform characteristics
- Would benefit from a section on "When converting across platforms" with stdlib, threading, and package manager considerations
- [ ] Include guidance on **9th pillar (REPL/Workflow)** for REPL-centric languages
- Scala, Elixir, Clojure, Erlang, Haskell all have strong REPL workflows
- This pillar is important for language pairs where both have interactive development
- Currently mentioned in create-lang-conversion-skill but not in meta-convert-dev
- [ ] Add section on **paradigm mental model shifts** as a first-class pattern
- OOP → FP, imperative → declarative, static → dynamic
- The Scala → Elixir conversion required significant mental model translation
- Could be a reusable pattern for other cross-paradigm conversions
- [ ] Expand **concurrency model comparison** beyond basic async/await
- Thread pools vs process pools vs event loops
- Shared state vs message passing
- Would help with Akka → OTP, async/await → Task, etc.

### Additional Notes
The meta-skill is comprehensive and well-structured. The suggested improvements are enhancements for cross-paradigm and cross-platform conversions, which are becoming more common.

Relates to #205

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Feedback from: `/create-lang-conversion-skill scala elixir`