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_catalog.go

@@ -60,12 +60,13 @@ var molCatalogCmd = &cobra.Command{
 			fmt.Println("  1. Create an epic with child issues")
 			fmt.Println("  2. Add the 'template' label: bd label add <epic-id> template")
 			fmt.Println("  3. Use {{variable}} placeholders in titles/descriptions")
-			fmt.Println("\nTo spawn (instantiate) a molecule from a proto:")
-			fmt.Println("  bd mol spawn <id> --var key=value")
+			fmt.Println("\nTo instantiate a molecule from a proto:")
+			fmt.Println("  bd pour <id> --var key=value          # persistent mol")
+			fmt.Println("  bd wisp create <id> --var key=value   # ephemeral wisp")
 			return
 		}
 
-		fmt.Printf("%s\n", ui.RenderPass("Protos (for bd mol spawn):"))
+		fmt.Printf("%s\n", ui.RenderPass("Protos (for bd pour / bd wisp create):"))
 		for _, mol := range molecules {
 			vars := extractVariables(mol.Title + " " + mol.Description)
 			varStr := ""