Say why an empty name is rejected, and finish what that removed

The reason given was wrong. A dot path did reach an empty-named field:
Fake("a.") returned it, Fake("a.b.") returned a nested one, and {..a.} bound
it. What was true is narrower — List never offered it, because an empty name
is no path segment — so the engine accepted spellings it would not advertise.
The message, the test comment and the README say that instead.

Two things the rejection finished off:

A {} token still reported "no field \"\"", pointing at a fix the loader now
rejects — two errors for one rule. It is told the name can never exist, like
an option token already is.

addressable is dead: both halves of "not empty and no dot" are now rejected
where a name is authored. Mutating it to panic leaves the suite green here
and panics on main, so it was live and is not. Keeping it would preserve the
silent-hiding this change removes — List quietly omitting a name rather than
New refusing it.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

fakes.go

@@ -22,7 +22,6 @@ import (
 	"fmt"
 	"math/rand/v2"
 	"sort"
-	"strings"
 )
 
 // Fakes generates fake data from a loaded namespace tree. Create one with [New].
@@ -93,14 +92,6 @@ func (f *Fakes) List() []string {
 	return out
 }
 
-// addressable reports whether a name can be one segment of a dot path. A dot would
-// split it into two segments and an empty name into none, so a path through such a
-// name cannot be spelled — List must not offer one, and it must not count towards
-// what a choice's variants share.
-func addressable(name string) bool {
-	return name != "" && !strings.Contains(name, ".")
-}
-
 // paths lists the dot paths addressable from n, relative to it, where "" is n
 // itself. A group has no value of its own, so it contributes only its children's.
 func paths(n node) []string {
@@ -108,9 +99,6 @@ func paths(n node) []string {
 	case *group:
 		var out []string
 		for _, name := range sortedNames(n.children) {
-			if !addressable(name) {
-				continue
-			}
 			for _, p := range paths(n.children[name]) {
 				out = append(out, join(name, p))
 			}
@@ -119,7 +107,7 @@ func paths(n node) []string {
 	case *template:
 		out := []string{""}
 		for _, name := range sortedNames(n.fields) {
-			if isRef(name) || !addressable(name) { // a binding, or unreachable by path
+			if isRef(name) { // a binding, not a path segment
 				continue
 			}
 			for _, p := range paths(n.fields[name]) {