docs: Clarify formulas are JSON, add distillation and sharing docs

- Fix YAML → JSON references in formula.go and types.go
- Update MOLECULES.md with ephemeral proto architecture
- Add Distillation section: extract formulas from completed work
- Add Sharing section: Mol Mall formula marketplace
- Update Layer Cake diagram to show ephemeral proto flow

Related: bd-1dez (Mol Mall epic)

🤖 Generated with [Claude Code](https://claude.com/claude-code)

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

internal/formula/types.go

@@ -249,16 +249,20 @@ type LoopSpec struct {
 // OnCompleteSpec defines actions triggered when a step completes (gt-8tmz.8).
 // Used for runtime expansion over step output (the for-each construct).
 //
-// Example YAML:
+// Example JSON:
 //
-//	step: survey-workers
-//	on_complete:
-//	  for_each: output.polecats
-//	  bond: mol-polecat-arm
-//	  vars:
-//	    polecat_name: "{item.name}"
-//	    rig: "{item.rig}"
-//	  parallel: true
+//	{
+//	  "id": "survey-workers",
+//	  "on_complete": {
+//	    "for_each": "output.polecats",
+//	    "bond": "mol-polecat-arm",
+//	    "vars": {
+//	      "polecat_name": "{item.name}",
+//	      "rig": "{item.rig}"
+//	    },
+//	    "parallel": true
+//	  }
+//	}
 type OnCompleteSpec struct {
 	// ForEach is the path to the iterable collection in step output.
 	// Format: "output.<field>" or "output.<field>.<nested>"