refactor: Switch formula format from YAML to JSON

- Change file extension from .formula.yaml to .formula.json
- Replace gopkg.in/yaml.v3 with encoding/json in parser
- Remove yaml struct tags, keep json tags only
- Update all test cases to use JSON format
- Update documentation references

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Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

docs/MOLECULES.md

@@ -238,7 +238,7 @@ bd wisp gc             # Garbage collect old wisps
 For reference, here's how the layers stack:
 
 ```
-Formulas (YAML compile-time macros)      ← optional, for complex composition
+Formulas (JSON compile-time macros)      ← optional, for complex composition
     ↓
 Protos (template issues)                  ← optional, for reusable patterns
     ↓