refactor(mol): remove bd mol spawn - use pour/wisp only (bd-8y9t)

Remove the spawn command from bd mol. Proto instantiation now uses:
- bd pour <proto> - Instantiate as persistent mol (liquid phase)
- bd wisp create <proto> - Instantiate as ephemeral wisp (vapor phase)

Rationale:
- 'spawn' doesn't fit the chemistry metaphor
- Two phase transitions (pour/wisp) are clearer than one command with flags
- Avoids confusion about defaults

Changes:
- Delete mol_spawn.go
- Update mol.go, mol_catalog.go, mol_distill.go to reference pour/wisp
- Update pour.go and wisp.go to remove 'Equivalent to spawn' comments
- Update info.go changelog entries
- Update CHANGELOG.md, ARCHITECTURE.md, DELETIONS.md

Closes bd-8y9t

cmd/bd/mol_distill.go

@@ -190,8 +190,8 @@ func runMolDistill(cmd *cobra.Command, args []string) {
 	if len(result.Variables) > 0 {
 		fmt.Printf("  Variables: %s\n", strings.Join(result.Variables, ", "))
 	}
-	fmt.Printf("\nTo spawn this proto:\n")
-	fmt.Printf("  bd mol spawn %s", result.ProtoID[:8])
+	fmt.Printf("\nTo instantiate this proto:\n")
+	fmt.Printf("  bd pour %s", result.ProtoID[:8])
 	for _, v := range result.Variables {
 		fmt.Printf(" --var %s=<value>", v)
 	}