fix(go): attach cross-file methods to their receiver type (#583) (#716)

Add a resolution-phase pass (goCrossFileMethodContainsEdges) that links a Go
method to its same-named receiver type within the same package (= directory),
so a method declared in a different file from its `type` is no longer orphaned
from the struct. Runs before goImplementsEdges so cross-file methods also count
toward interface satisfaction (#584). Adds a regression test + CHANGELOG entry.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

CHANGELOG.md

@@ -69,6 +69,7 @@ and adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0.html).
 - TypeScript `.mts` and `.cts` module files are now indexed instead of being skipped. (#366)
 - JavaScript modules that wrap their code in an anonymous function — AMD/RequireJS, NetSuite SuiteScript, IIFE bundles — now have their inner functions and calls indexed, instead of the file coming up nearly empty. (#528)
 - Go methods declared on generic types (e.g. `func (s *Stack[T]) Push(...)`) are now correctly attached to their type, so callers, callees, and impact include them. (#583)
+- Go methods now attach to their receiver type even when declared in a different file from the `type` itself — the idiomatic split where `type User struct{…}` lives in one file and `func (u *User) Save()` in another. Previously a cross-file method was orphaned from its struct, so the type's member list, callers/callees, and impact missed it; as a knock-on, a struct whose interface-satisfying methods are spread across files now also links to the interfaces it implements. (#583)
 - Asking what a symbol impacts no longer drags in every unrelated sibling method of its class — impact now follows real dependencies instead of the structural "contains" relationship, keeping the result focused on what actually depends on the symbol. (#536)
 - CodeGraph's MCP server now answers an agent's `resources/list` and `prompts/list` probes with an empty list instead of an error, clearing the `-32601` messages some clients (opencode, Codex) logged on connect. (#621)
 - Svelte and Vue components used through a barrel file — `export { default as Button } from './Button.svelte'` re-exported from an `index.ts` and imported elsewhere — are no longer falsely reported as having **0 callers**. CodeGraph now follows the default re-export all the way to the component and resolves the imports that `.svelte` / `.vue` files themselves use, so `codegraph_callers` and `codegraph_impact` see every place a component is used. This also covers components imported from another package in a workspace/monorepo (`@scope/ui/widgets`) and bare directory imports (`import { x } from './'`). Previously a live component consumed only through a barrel looked like dead code. Thanks @nakisen. (#629)