feat: executions, assertions y bucle reactivo en fn_operations

Añade Execution, Assertion, AssertionResult al paquete fn_operations.
Motor de evaluación de assertions con reescritura SQL automática.
Bucle reactivo: ExecuteAndReact evalúa assertions y cambia status de
entities (corrupted/stale) + auto-crea proposals en registry.
CLI fn ops: assertion (add/list/show/delete/eval) y execution (add/list/show).
Migración 002_executions_assertions.sql con FTS para assertions.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

cmd/fn/main.go

@@ -31,6 +31,8 @@ func main() {
 		cmdAdd(os.Args[2:])
 	case "ops":
 		cmdOps(os.Args[2:])
+	case "proposal":
+		cmdProposal(os.Args[2:])
 	case "help", "-h", "--help":
 		printUsage()
 	default:
@@ -49,7 +51,8 @@ Usage:
   fn list   [-k kind] [-d domain] [-l lang]
   fn show   <id>                           Muestra entrada completa
   fn add    [-k kind]                      Abre $EDITOR con template
-  fn ops    <subcommand>                   Gestiona operations.db (fn ops help)`)
+  fn ops    <subcommand>                   Gestiona operations.db (fn ops help)
+  fn proposal <add|list|show|update>       Gestiona proposals`)
 }
 
 func root() string {