Fix source file links for non-GitHub hosts (e.g. Azure DevOps)

[jirisacha]

Problem

On a wiki page, the "Sources" footer renders file links that point to a
non-existent github.com repository when the repository is not hosted on
GitHub (Azure DevOps, self-hosted GitLab, etc.).

Example (Azure DevOps repo): the footer links to
https://github.com/{owner}/{repo}/blob/{branch}/{file} — a 404 — while the
in-content "Related Links" / source-attribution links on the same page point
to the correct Azure DevOps URL.

Root cause

The two kinds of links are built by two different code paths:

• In-content links are baked server-side into the stored Markdown by
  WikiGenerator.BuildGitFileBaseUrl, which already detects the hosting
  platform (GitHub / GitLab / Gitee / Bitbucket / Azure DevOps). ✅ correct.
• The "Sources" footer is built client-side by the SourceFiles
  component, which diverged:
  1. It was never passed the repository git URL, so it fabricated
     https://github.com/${owner}/${repo} from the route params
     (source-files.tsx). For non-GitHub repos this is a dead link.
  2. buildFileUrl had no Azure DevOps case, so even with a real git URL
     it fell back to the GitHub /blob/ format, which is invalid for ADO.

The docs API (RepositoryDocResponse) did not expose the repository git URL,
so the component had nothing correct to use.

Fix

• Backend: return GitUrl and Branch from the docs API
  (RepositoryDocResponse, populated in RepositoryDocsService.GetDocAsync
  from the repository entity and the resolved branch).
• Frontend: thread gitUrl and branch into SourceFiles; add an Azure
  DevOps format to buildFileUrl (?version=GB{branch}&path=/{file},
  mirroring the backend); and remove the hardcoded github.com fallback — when
  the git URL is unknown the file is shown as a plain label instead of a broken
  link.

Notes

• No data migration required: footer links are computed at render time, so the
  fix retroactively corrects all existing repositories. Stored content is
  unchanged.
• GitHub-hosted repositories keep the existing /blob/ behaviour.

Verification

• dotnet build — 0 errors.
• Frontend tsc --noEmit and eslint on the changed files — clean.