Fix ITocGeneratorService resolution in tiered Docs applications

[maliming]

Move the Docs TableOfContents presentation helper back to the Web layer so ITocGeneratorService resolves in tiered applications; it is a rendering helper, not a remote application service.

Reported by @LEIRONGHUA in #25796.

[Copilot]

Pull request overview

This PR addresses DI resolution issues for ITocGeneratorService in tiered/layered Docs applications by relocating the Table of Contents (TOC) generation helper into the Web layer and ensuring it’s no longer treated as a remote application service.

Changes:

• Added TOC model types (TocHeading, TocItem) and a Web-layer TocGeneratorService implementation.
• Updated ITocGeneratorService to no longer inherit from IApplicationService (so it’s not considered a remote app service).
• Updated Volo.Docs.Application.abppkg.analyze.json to remove the TOC generator from the Application module’s analyzed “applicationService” contents.

Reviewed changes

Copilot reviewed 2 out of 4 changed files in this pull request and generated no comments.

File	Description
modules/docs/src/Volo.Docs.Web/TableOfContents/TocHeading.cs	Introduces TOC heading/tree model types used by the Web UI.
modules/docs/src/Volo.Docs.Web/TableOfContents/TocGeneratorService.cs	Adds a Web-layer TOC generation service based on Markdig parsing.
modules/docs/src/Volo.Docs.Web/TableOfContents/ITocGeneratorService.cs	Removes IApplicationService inheritance so the TOC helper is not treated as a remote service.
modules/docs/src/Volo.Docs.Application/Volo.Docs.Application.abppkg.analyze.json	Removes TOC generator service metadata from Application module analysis output.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 49.36%. Comparing base (cafda7a) to head (4fb0403).
⚠️ Report is 21 commits behind head on rel-10.6.

Additional details and impacted files

@@             Coverage Diff              @@
##           rel-10.6   #25799      +/-   ##
============================================
+ Coverage     49.06%   49.36%   +0.30%     
============================================
  Files          3738     3687      -51     
  Lines        126821   124434    -2387     
  Branches       9753     9508     -245     
============================================
- Hits          62223    61430     -793     
+ Misses        62728    61151    -1577     
+ Partials       1870     1853      -17     

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