fix(javascript): analyze sources containing empty string literals

A single legal empty literal such as `fetch('')`, `require('')`,
`bus.on('', f)`, `localStorage.getItem('')`, or `ipcMain.handle('', f)`
made the whole application analysis fail with `unreadable_output`: the
literal became an application-graph observation label, an artifact-local
identity key, or a semantic node label, all of which must be nonempty.

Normalize display at the two graph construction seams instead of at each
producer: `JavaScriptArtifactGraphAccumulator.addNode` and
`constructSemanticGraphNode` show the empty value as `""` via a shared
`javascriptDisplayText` helper. Observation and node properties keep the
exact empty value. This replaces the per-site `semanticNameLabel` calls.

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

src/application/JavaScriptSemanticGraphConstruction.ts

@@ -1,5 +1,6 @@
 import type { JavaScriptApplicationGraph } from "../domain/javascriptApplicationGraph.js";
 import type { JsonValue } from "../domain/jsonValue.js";
+import { javascriptDisplayText } from "../domain/javascriptAstValues.js";
 import {
   createJavaScriptSemanticGraphNode,
   createJavaScriptSemanticGraphRelation,
@@ -18,14 +19,6 @@ 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>;
@@ -85,7 +78,7 @@ export const constructSemanticGraphNode = (
     },
     function_node_id: input.functionNodeId,
     application_node_ids: matchingApplicationNodeIds(file, input, state),
-    label: input.label,
+    label: input.label === null ? null : javascriptDisplayText(input.label),
     properties: input.properties ?? {},
     evidence: observedSemanticEvidence(file, input.location),
   });