fix(javascript): keep exact empty env keys and method names

`process.env['']` now projects an exact empty environment key with
complete resolution instead of the same null/partial result as a dynamic
`process.env[key]`. `{ ['']() {} }` keeps its exact empty method name in
the IR instead of a generated `[computed@N]` name.

Semantic graph labels stay nonempty: a shared `semanticNameLabel` helper
displays the empty key as `""` for property slots, config sources, and
function nodes, while `properties.key` keeps the exact value.

Refs #783

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

src/application/JavaScriptSemanticGraphConstruction.ts

@@ -18,6 +18,14 @@ import {
   unavailableSemanticRootEvidence,
 } from "./JavaScriptSemanticGraphEvidence.js";
 
+/**
+ * Display an exact JavaScript key or name as a nonempty graph label. The legal
+ * empty key is shown as `""`; callers keep the exact value where the node
+ * carries it.
+ */
+export const semanticNameLabel = (name: string): string =>
+  name === "" ? '""' : name;
+
 /** Mutable local projection state hidden from graph callers. */
 export interface SemanticGraphProjectionState {
   readonly nodes: Map<string, JavaScriptSemanticGraphNode>;