build(deps): bump actions/cache from 4 to 5

Bumps [actions/cache](https://github.com/actions/cache) from 4 to 5.
- [Release notes](https://github.com/actions/cache/releases)
- [Changelog](https://github.com/actions/cache/blob/main/RELEASES.md)
- [Commits](actions/cache@v4...v5)

---
updated-dependencies:
- dependency-name: actions/cache
  dependency-version: '5'
  dependency-type: direct:production
  update-type: version-update:semver-major
...

Signed-off-by: dependabot[bot] <support@github.com>

Author: dependabot[bot]

.github/workflows/_hugo.yml

@@ -31,7 +31,7 @@ jobs:
         uses: actions/configure-pages@v5
 
       # Tier 1: Dependencies cache (changes infrequently)
-      - uses: actions/cache@v4
+      - uses: actions/cache@v5
         name: Cache dependencies
         with:
           path: |
@@ -45,7 +45,7 @@ jobs:
       - run: bun install
 
       # Tier 2: Hugo build cache (changes with any build-affecting file)
-      - uses: actions/cache@v4
+      - uses: actions/cache@v5
         name: Cache Hugo build resources
         with:
           path: |
@@ -57,7 +57,7 @@ jobs:
             ${{ runner.os }}-hugo-
 
       # Tier 3: Content and template cache (comprehensive file tracking)
-      - uses: actions/cache@v4
+      - uses: actions/cache@v5
         name: Cache Hugo content and assets
         with:
           path: |