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

docs/DELETIONS.md

@@ -202,7 +202,7 @@ The 1-hour grace period ensures tombstones propagate even with minor clock drift
 
 ## Wisps: Intentional Tombstone Bypass
 
-**Wisps** (ephemeral issues created by `bd mol spawn`) are intentionally excluded from tombstone tracking.
+**Wisps** (ephemeral issues created by `bd wisp create`) are intentionally excluded from tombstone tracking.
 
 ### Why Wisps Don't Need Tombstones