feat(cmd): wire VCS detection into main — route to github or gitea client

- Replace gitea.NewClient() with newVCSClient(vcsType, vcsURL, token)
- Replace newGiteaClientAdapter() with buildRepoPersonaClient()
- Remove now-redundant giteaClientAdapter struct (moved to vcs.go)
- Update fetchFileContext and fetchPatterns to accept vcsClient interface
- Log detected VCS type at startup

On Gitea runners: behaves identically to before (gitea.NewClient).
On GitHub/GHES runners: uses githubAdapter backed by github.Client,
  all API calls use GitHub REST API v3 with GITHUB_API_URL as base URL.

cmd/review-bot/main.go

@@ -168,8 +168,12 @@ func main() {
 		os.Exit(1)
 	}
 
+	// Detect VCS type and initialize the appropriate client.
+	vcsType := detectVCSType()
+	slog.Info("detected VCS type", "vcs", vcsType)
+
 	// Initialize clients
-	giteaClient := gitea.NewClient(*vcsURL, *reviewerToken)
+	giteaClient := newVCSClient(vcsType, *vcsURL, *reviewerToken)
 	llmClient := llm.NewClient(*llmBaseURL, *llmAPIKey, *llmModel)
 	if *llmTemp < 0 || *llmTemp > 2 {
 		slog.Error("invalid LLM temperature", "temperature", *llmTemp, "range", "0-2")
@@ -207,7 +211,7 @@ func main() {
 	var persona *review.Persona
 	if *personaName != "" {
 		// Try loading from repo first, then fall back to built-in
-		repoPersonas, err := review.LoadRepoPersonas(ctx, newGiteaClientAdapter(giteaClient), owner, repoName)
+		repoPersonas, err := review.LoadRepoPersonas(ctx, buildRepoPersonaClient(giteaClient), owner, repoName)
 		if err != nil {
 			slog.Warn("could not load repo personas", "repo", owner+"/"+repoName, "error", err)
 			// Continue with built-in personas only.
@@ -527,7 +531,7 @@ func main() {
 }
 
 // fetchFileContext fetches the full content of modified files from the PR branch.
-func fetchFileContext(ctx context.Context, client *gitea.Client, owner, repo, ref string, files []gitea.ChangedFile) string {
+func fetchFileContext(ctx context.Context, client vcsClient, owner, repo, ref string, files []gitea.ChangedFile) string {
 	var sb strings.Builder
 	for _, f := range files {
 		if ctx.Err() != nil {
@@ -554,7 +558,7 @@ func fetchFileContext(ctx context.Context, client *gitea.Client, owner, repo, re
 // patternsFiles is comma-separated list of file paths or directories.
 // If a path ends with / or is a directory, all files within it are fetched recursively.
 // If patternsFiles is empty, all files from the repo root are fetched.
-func fetchPatterns(ctx context.Context, client *gitea.Client, patternsRepo, patternsFiles string) string {
+func fetchPatterns(ctx context.Context, client vcsClient, patternsRepo, patternsFiles string) string {
 	var sb strings.Builder
 
 	repos := strings.Split(patternsRepo, ",")
@@ -851,31 +855,3 @@ func shouldSkipStaleReview(evaluatedSHA, currentSHA string) bool {
 	return evaluatedSHA != currentSHA
 }
 
-// giteaClientAdapter adapts gitea.Client to review.GiteaClient interface.
-type giteaClientAdapter struct {
-	client *gitea.Client
-}
-
-func newGiteaClientAdapter(c *gitea.Client) *giteaClientAdapter {
-	return &giteaClientAdapter{client: c}
-}
-
-func (a *giteaClientAdapter) ListContents(ctx context.Context, owner, repo, path string) ([]review.ContentEntry, error) {
-	entries, err := a.client.ListContents(ctx, owner, repo, path)
-	if err != nil {
-		return nil, err
-	}
-	result := make([]review.ContentEntry, len(entries))
-	for i, e := range entries {
-		result[i] = review.ContentEntry{
-			Name: e.Name,
-			Path: e.Path,
-			Type: e.Type,
-		}
-	}
-	return result, nil
-}
-
-func (a *giteaClientAdapter) GetFileContent(ctx context.Context, owner, repo, filepath string) (string, error) {
-	return a.client.GetFileContent(ctx, owner, repo, filepath)
-}