fix: regenerate file-router files when layouts changes

[mcollovati]

Description

The layouts file can be updated by Flow at runtime when an annotated layout class is modified and reloaded.
This change forces the Vite file-router plugin to regenerate files and trigger a fs-route-update to refresh the client configuration.

Type of change

• Bugfix
• Feature

Checklist

• I have read the contribution guide: https://vaadin.com/docs/latest/guide/contributing/overview/
• I have added a description following the guideline.
• The issue is created in the corresponding repository and I have referenced it.
• I have added tests to ensure my change is effective and works as intended.
• New and existing tests are passing locally with my change.
• I have performed self-review and corrected misspellings.

Additional for Feature type of change

• Enhancement / new feature was discussed in a corresponding GitHub issue and Acceptance Criteria were created.

[sonarcloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarCloud

[codecov]

Codecov Report

Attention: Patch coverage is 0% with 1 line in your changes missing coverage. Please review.

Project coverage is 92.26%. Comparing base (ee782b2) to head (f434639).

Files with missing lines	Patch %	Lines
packages/ts/file-router/src/vite-plugin.ts	0.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #2796      +/-   ##
==========================================
- Coverage   92.29%   92.26%   -0.04%     
==========================================
  Files          81       81              
  Lines        2675     2676       +1     
  Branches      685      686       +1     
==========================================
  Hits         2469     2469              
- Misses        156      157       +1     
  Partials       50       50              

Flag	Coverage Δ
unittests	92.26% <0.00%> (-0.04%)	⬇️

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