Fix GitHub Pages API docs generation for net9.0

[Copilot]

The GitHub Pages docs workflow was publishing successfully, but the API reference under api/ was not being generated. DocFX was still configured against a stale net8.0 DLL path, so the published site omitted the managed API docs.

• Align DocFX metadata with the project

  • Point DocFX at KartaViewSharp/KartaViewSharp.csproj instead of a hard-coded build output path
  • Update DocFX metadata generation to target net9.0

• Align the docs workflow with the repository SDK

  • Update the Pages/docs workflow to install the .NET 9 SDK before building and running DocFX

• Result

  • Restores managed-reference generation so the api/ section is produced and published to GitHub Pages again

{
  "src": [
    {
      "src": ".",
      "files": [ "KartaViewSharp/KartaViewSharp.csproj" ]
    }
  ],
  "dest": "api",
  "properties": {
    "TargetFramework": "net9.0"
  }
}

[codacy-production]

Up to standards ✅

🟢 Issues 0 issues

Results:
0 new issues

View in Codacy

🟢 Coverage ∅ diff coverage · +0.46% coverage variation

Metric	Results
Coverage variation	✅ +0.46% coverage variation (-1.00%)
Diff coverage	✅ ∅ diff coverage

View coverage diff in Codacy

Coverage variation details

	Coverable lines	Covered lines	Coverage
Common ancestor commit (123bbe6)	989	260	26.29%
Head commit (b7ad6e1)	13221 (+12232)	3536 (+3276)	26.75% (+0.46%)

Coverage variation is the difference between the coverage for the head and common ancestor commits of the pull request branch: <coverage of head commit> - <coverage of common ancestor commit>

Diff coverage details

	Coverable lines	Covered lines	Diff coverage
Pull request (#104)	0	0	∅ (not applicable)

Diff coverage is the percentage of lines that are covered by tests out of the coverable lines that the pull request added or modified: <covered lines added or modified>/<coverable lines added or modified> * 100%

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TIP This summary will be updated as you push new changes.}

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[sonarqubecloud]

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 SonarQube Cloud