fix(install): fix CI test failures for nested overrides

- Fix ban-words test: replace '= undefined' with initialized default in
  ResolutionSegments struct
- Update yarn-lock-migration snapshot: 'webpack/acorn' resolution is now
  correctly represented as a nested override
- Update pnpm-comprehensive snapshot: version-scoped override
  'negotiator@>0.6.0' ordering changed due to tree-based serialization

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

src/install/lockfile/OverrideMap.zig

@@ -892,7 +892,7 @@ pub fn parseFromResolutions(
 }
 
 const ResolutionSegments = struct {
-    segments: [8][]const u8 = undefined,
+    segments: [8][]const u8 = .{""} ** 8,
     count: usize = 0,
     last: []const u8 = "",
     overflow: bool = false,

test/cli/install/migration/__snapshots__/pnpm-comprehensive.test.ts.snap

@@ -263,8 +263,8 @@ exports[`pnpm comprehensive migration tests pnpm with patches and overrides: pat
     "express@4.18.2": "patches/express@4.18.2.patch",
   },
   "overrides": {
-    "mime-types": "2.1.33",
     "negotiator@>0.6.0": "0.6.2",
+    "mime-types": "2.1.33",
   },
   "packages": {
     "accepts": ["accepts@1.3.8", "", { "dependencies": { "mime-types": "2.1.33", "negotiator": "0.6.2" } }, "sha512-acceptsAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA=="],

test/cli/install/migration/__snapshots__/yarn-lock-migration.test.ts.snap

@@ -206,6 +206,9 @@ exports[`yarn.lock migration basic yarn.lock with resolutions: resolutions-yarn-
     },
   },
   "overrides": {
+    "webpack": {
+      "acorn": "8.11.2",
+    },
     "acorn": "8.11.3",
   },
   "packages": {