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/info.go

@@ -341,9 +341,9 @@ var versionChanges = []VersionChange{
 		Version: "0.33.0",
 		Date:    "2025-12-21",
 		Changes: []string{
-			"NEW: Wisp molecules (bd-2vh3) - bd mol spawn creates wisp issues by default",
+			"NEW: Wisp molecules (bd-2vh3) - use 'bd wisp create' for ephemeral wisps",
 			"NEW: Wisp issues live only in SQLite, never export to JSONL (prevents zombie resurrection)",
-			"NEW: --persistent flag on bd mol spawn to opt out of wisp spawning",
+			"NEW: Use 'bd pour' for persistent mols, 'bd wisp create' for ephemeral wisps",
 			"NEW: bd mol squash compresses wisp children into digest issue",
 			"NEW: --summary flag on bd mol squash for agent-provided AI summaries",
 			"FIX: DeleteIssue now cascades to comments table (bd-687g)",