fix: Hugo package naming fix (#688)

## Summary

Rebases the Hugo package naming fix from #609 on top of the current
`main` branch, including the installer flow added in #687.

- Derive Hugo release asset OS and architecture naming conventions from
the requested Hugo version.
- Apply those conventions when selecting OS and architecture segments,
including the 0.102.x macOS universal boundary, 0.103+ downcased OS
names, Windows zip assets, and Linux ARM assets.
- Add table-driven tests for pre-0.102, 0.102.x, and 0.103+ naming
behavior, plus URL coverage for the corrected release asset names.

## Changes

- Add `getConventions` to centralize version-based release asset naming
decisions.
- Update `getOS` and `getArch` to use convention flags for macOS,
lower-case OS names, standardized architecture names, and the Windows
ARM support boundary.
- Update `getURL` to generate candidate URLs for downcased Windows and
Linux assets, and for darwin universal archives.
- Wire convention detection into `installer` before generating candidate
Hugo release asset URLs.
- Expand unit coverage for OS, architecture, convention, and URL
behavior.

## Checklist

- [x] I have read the latest README and followed the instructions.
- [x] I have added or updated tests for behavior changes.
- [x] README.md and action.yml updates are not needed because inputs and
action metadata are unchanged.
- [x] I have run the relevant verification commands.

## References

- Rebased follow-up for
https://github.com/peaceiris/actions-hugo/pull/609
- References https://github.com/peaceiris/actions-hugo/issues/605 and
https://github.com/peaceiris/actions-hugo/issues/608
- Based on `main` after
https://github.com/peaceiris/actions-hugo/pull/687

## Verification

- [x] `RUNNER_TEMP=/private/tmp npm run all`
- [ ] `npm run build` was not run because this branch does not update
bundled output and current `main` removed `lib/index.js`.


<!-- This is an auto-generated comment: release notes by coderabbit.ai
-->
## Summary by CodeRabbit

* **New Features**
* Version-aware conventions control OS and architecture naming,
including macOS universal asset support and expanded darwin/macOS
patterns.

* **Refactor**
* Conventions centralized and applied across installer and URL
generation; OS/arch inputs accept varied casing and naming variants.

* **Tests**
* Expanded, data-driven parameterized tests for conventions, OS/arch
mappings, URL variants, and error cases.
* Replaced network stubs with deterministic fetch-mock helpers for test
isolation.

[![Review Change
Stack](https://storage.googleapis.com/coderabbit_public_assets/review-stack-in-coderabbit-ui.svg)](https://app.coderabbit.ai/change-stack/peaceiris/actions-hugo/pull/688)
<!-- end of auto-generated comment: release notes by coderabbit.ai -->

---------

Co-authored-by: Michael T Lombardi <michael.t.lombardi@gmail.com>
Co-authored-by: codefactor-io <support@codefactor.io>
Co-authored-by: Codex <noreply@openai.com>

__tests__/get-os.test.ts

@@ -1,15 +1,100 @@
 import getOS from '../src/get-os';
 
 describe('getOS', () => {
-  test('os type', () => {
-    expect(getOS('linux')).toBe('Linux');
-    expect(getOS('darwin')).toBe('macOS');
-    expect(getOS('win32')).toBe('Windows');
+  const groups = [
+    {
+      condition: 'when hugo version < 0.102.0',
+      conventions: {
+        arch: {
+          darwinUniversal: false,
+          droppedWindowsArmSupport: false,
+          standardizedNaming: false
+        },
+        os: {
+          renamedMacOS: false,
+          downcasedAll: false
+        }
+      },
+      tests: [
+        {os: 'linux', expected: 'Linux'},
+        {os: 'darwin', expected: 'macOS'},
+        {os: 'win32', expected: 'Windows'}
+      ]
+    },
+    {
+      condition: 'when hugo version === 0.102.z',
+      conventions: {
+        arch: {
+          darwinUniversal: true,
+          droppedWindowsArmSupport: true,
+          standardizedNaming: false
+        },
+        os: {
+          renamedMacOS: false,
+          downcasedAll: false
+        }
+      },
+      tests: [
+        {os: 'linux', expected: 'Linux'},
+        {os: 'darwin', expected: 'macOS'},
+        {os: 'win32', expected: 'Windows'}
+      ]
+    },
+    {
+      condition: 'when hugo version >= 0.103.0',
+      conventions: {
+        arch: {
+          darwinUniversal: true,
+          droppedWindowsArmSupport: true,
+          standardizedNaming: true
+        },
+        os: {
+          renamedMacOS: true,
+          downcasedAll: true
+        }
+      },
+      tests: [
+        {os: 'linux', expected: 'linux'},
+        {os: 'darwin', expected: 'darwin'},
+        {os: 'win32', expected: 'windows'}
+      ]
+    }
+  ].map(function (group) {
+    group.tests = group.tests.map(function (example) {
+      return Object.assign(example, {
+        toString: function () {
+          return `${example.os} returns ${example.expected}`;
+        }
+      });
+    });
+    return Object.assign(group, {
+      toString: function () {
+        return group.condition;
+      }
+    });
+  });
+
+  describe.each(groups)('%s', ({conventions, tests}) => {
+    test.each(tests)('%s', ({os, expected}) => {
+      expect(getOS(os, conventions)).toBe(expected);
+    });
   });
 
   test('exception', () => {
+    const conventions = {
+      arch: {
+        darwinUniversal: false,
+        droppedWindowsArmSupport: false,
+        standardizedNaming: false
+      },
+      os: {
+        renamedMacOS: false,
+        downcasedAll: false
+      }
+    };
+
     expect(() => {
-      getOS('centos');
+      getOS('centos', conventions);
     }).toThrow('centos is not supported');
   });
 });