fix(head): resolve reactive input before pushing to unhead

[Carpediem94]

Fixes #1004

🔗 Linked issue

Issue #1004

❓ Type of change

• 📖 Documentation (updates to the documentation or readme)
• 🐞 Bug fix (a non-breaking change that fixes an issue)
• 👌 Enhancement (improving an existing functionality)
• ✨ New feature (a non-breaking change that adds functionality)
• 🧹 Chore (updates to the build process or auxiliary tools and libraries)
• ⚠️ Breaking change (fix or feature that would cause existing functionality to change)

📚 Description

@unhead/vue's clientUseHead resolves reactive input with walkResolver(input, VueResolver) inside a watchEffect before pushing an entry. The composable this module registers in its place pushed the raw input, and the client head has no prop resolver of its own — @unhead/vue/server is the only one created with propResolvers: [VueResolver], which is why this never showed up during SSR.

I used Claude Opus 5 to analyze the problem and find a possible solution, before submit PR I review the code and make some changes on my own (I prefer to let "claude contribute" in the commit for transparency).
Currently I have already a workaround on my business projects to fix this error, so I decide to contribute to the repository.

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[codecov]

Codecov Report

❌ Patch coverage is 0% with 14 lines in your changes missing coverage. Please review.
✅ Project coverage is 28.10%. Comparing base (55664b7) to head (6355f95).

Files with missing lines	Patch %	Lines
src/runtime/composables/head.ts	0.00%	14 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1005      +/-   ##
==========================================
- Coverage   28.96%   28.10%   -0.86%     
==========================================
  Files          12       12              
  Lines         328      338      +10     
  Branches       98      100       +2     
==========================================
  Hits           95       95              
- Misses        233      243      +10     

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