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

CHANGELOG.md

@@ -156,10 +156,10 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 ### Added
 
-- **Wisp molecules** (bd-2vh3) - Spawn molecules as wisps by default
-  - `bd mol spawn` creates wisp issues that live only in SQLite
+- **Wisp molecules** (bd-2vh3) - Support for ephemeral wisps
+  - `bd wisp create` creates wisp issues that live only in SQLite
   - Wisp issues never export to JSONL (prevents zombie resurrection)
-  - Use `--persistent` flag to opt out of wisp spawning
+  - Use `bd pour` for persistent mols, `bd wisp create` for ephemeral wisps
   - `bd mol squash` compresses wisp children into a digest issue
   - `--summary` flag allows agents to provide AI-generated summaries