fix(resolution): Go cross-package qualified calls resolve via go.mod (#388) (#469)

`pkga.FuncX(...)` cross-package calls in Go monorepos were dropping
through the import resolver — `isExternalImport(go)` flagged any
non-`/internal/` import as third-party because the resolver had no idea
what the project's own module path was. Resolution fell back to name
matching with path-proximity scoring, which on a layered codebase picks
one accidental candidate per call site (~<1% recall per #388's
5,303-vs-1 figure).

- `src/resolution/go-module.ts` (new) parses the `module ...` directive
  from project-root `go.mod`, exposed via `getGoModule()` on
  `ResolutionContext`.
- `isExternalImport(go)` treats `<module-path>/...` imports as in-module;
  the existing `/internal/` escape hatch is preserved for repos without
  a parsed go.mod.
- `resolveViaImport` gets a Go cross-package branch that strips the
  module prefix to a project-relative directory, then resolves the
  qualified member via `getNodesByName(member)` filtered to that exact
  directory and `isExported=true`. Sub-packages don't collide with their
  parents; same-name funcs in different packages don't false-merge.
- Go extractor sets `isExported` from the identifier's first character
  (Go's universal uppercase=exported convention). The resolver depends
  on this to filter candidates.

Validation on gRPC-Go (1,031 .go files, layered package tree):
  total `calls` edges:    23,803 -> 34,105 (+43%)
  cross-pkg `calls`:      10,880 -> 19,929 (+83%)
  fmt/strconv/etc. stdlib calls: stay external (no false positives)

Tests cover in-module disambiguation with same-name funcs in two
packages, aliased imports, and stdlib calls not being false-resolved to
in-project nodes.

Closes #388.

src/resolution/index.ts

@@ -21,6 +21,7 @@ import { resolveViaImport, extractImportMappings, extractReExports } from './imp
 import { detectFrameworks } from './frameworks';
 import { synthesizeCallbackEdges } from './callback-synthesizer';
 import { loadProjectAliases, type AliasMap } from './path-aliases';
+import { loadGoModule, type GoModule } from './go-module';
 import { logDebug } from '../errors';
 import type { ReExport } from './types';
 import { LRUCache } from './lru-cache';
@@ -157,6 +158,8 @@ export class ReferenceResolver {
   // `null` = computed and absent. Treated as immutable for the
   // resolver's lifetime; callers re-create the resolver if config changes.
   private projectAliases: AliasMap | null | undefined = undefined;
+  // go.mod module path. Same lazy/immutable convention as projectAliases.
+  private goModule: GoModule | null | undefined = undefined;
 
   constructor(projectRoot: string, queries: QueryBuilder) {
     this.projectRoot = projectRoot;
@@ -370,6 +373,13 @@ export class ReferenceResolver {
         return this.projectAliases;
       },
 
+      getGoModule: () => {
+        if (this.goModule === undefined) {
+          this.goModule = loadGoModule(this.projectRoot);
+        }
+        return this.goModule;
+      },
+
       getReExports: (filePath: string, language) => {
         const cached = this.reExportCache.get(filePath);
         if (cached) return cached;