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/JavaScriptSemanticGraphBuilder.ts

@@ -48,7 +48,6 @@ import {
   addSemanticGraphRelation as addRelation,
   constructSemanticGraphNode as semanticNode,
   createSemanticGraphProjectionState as emptyState,
-  semanticNameLabel,
   type SemanticGraphProjectionState as BuilderState,
 } from "./JavaScriptSemanticGraphConstruction.js";
 
@@ -166,8 +165,7 @@ const projectFile = (
             kind: "function",
             roleKey: `callable:${callable.callableId}`,
             location: callable.location,
-            label:
-              callable.name === null ? null : semanticNameLabel(callable.name),
+            label: callable.name,
             functionNodeId: null,
           },
           state,