fix(audit): sort milestones, sort JSON export, extract test helper

- Fix milestone section using unsorted repos list
- Apply --sort to --format json output
- Rename _sort_repos to sort_repos (now used by cli.py)
- Extract shared make_repo helper to tests/helpers.py
- Move exporter import to module level in cli.py

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

src/gitea_dashboard/display.py

@@ -93,7 +93,7 @@ def _colorize_milestone_due(due_on: str | None) -> str:
     return "green"
 
 
-def _sort_repos(repos: list[RepoData], sort_key: str) -> list[RepoData]:
+def sort_repos(repos: list[RepoData], sort_key: str) -> list[RepoData]:
     """Trie la liste des repos selon le critere donne.
 
     Args:
@@ -144,7 +144,7 @@ def render_dashboard(
         return
 
     # Tri des repos
-    sorted_repos = _sort_repos(repos, sort_key)
+    sorted_repos = sort_repos(repos, sort_key)
 
     # Tableau principal
     table = Table(title="Gitea Dashboard")
@@ -172,7 +172,7 @@ def render_dashboard(
     console.print(table)
 
     # Section milestones — uniquement si au moins un repo en a
-    repos_with_milestones = [r for r in repos if r.milestones]
+    repos_with_milestones = [r for r in sorted_repos if r.milestones]
 
     if repos_with_milestones:
         console.print()