feat(javascript): link assignment right-hand sides to their writes (#6206)

* feat(javascript): link assignment right-hand sides to their writes

A declaration carries its value forward, but a later assignment to a
variable, a property or through a compound operator stopped the forward
trace at the right-hand-side read. The semantic IR now records one
syntactic assignment flow per simple assignment target (ranges, operator,
owning callable), and the graph projection connects each retained read
of the right-hand side to the write occurrence through a defines
relation. Compound assignments also consume the previous value of the
target; the written value itself stays unknown, keeping the boundary of
#4342 intact.

Fixes #6193

* fix(javascript): preserve computed key assignment ownership

* test(javascript): retain nested callback assignment ownership

* docs(javascript): record assignment influence verification

* test(mcp): isolate mocks and acknowledge cancellation boundaries

* test(javascript): retain CLI diagnostics and current-main verification

---------

Co-authored-by: gensokyo-dev <342580529+gensokyo-dev@users.noreply.github.com>

src/domain/javascript/javascriptSemanticProjection.ts

@@ -45,6 +45,7 @@ import {
   type CommonJsExportSite,
 } from "./javascriptCommonJsExportReceivers.js";
 import type { JavaScriptSemanticPropertyPath } from "./javascriptSemanticPropertyPaths.js";
+import { semanticComputedMethodKey } from "./javascriptSemanticEvaluationOrder.js";
 
 interface CollectCallableInput {
   readonly node: t.Node;
@@ -71,6 +72,12 @@ export const collectSemanticCallable = (input: CollectCallableInput): void => {
         ? null
         : bodyScope.scopeId,
     location: range(node),
+    computedKeyLocation:
+      "key" in node &&
+      t.isNode(node.key) &&
+      semanticComputedMethodKey(node, node.key)
+        ? range(node.key)
+        : null,
     returnSites: [],
     returnCoverage: {
       status: "partial",