Implement the higher-level GitHub API methods that were TODO since
issue #120. The github package now provides:

- GetPullRequest: PR metadata (title, body, head SHA/ref, draft)
- GetPullRequestDiff: unified diff via Accept: application/vnd.github.diff
- GetPullRequestFiles: changed files list (paginated, 100/page)
- GetCommitStatuses: CI statuses (GitHub uses 'state' field, normalized)
- GetFileContent: file content with base64 decode (strips embedded newlines)
- GetFileContentRef: file at a specific ref
- ListContents: directory listing or single-file normalization
- GetAllFilesInPath: recursive file fetching
- PostReview: submit review with event/body/commit/inline comments
- ListReviews: list PR reviews (paginated)
- DeleteReview: delete review (GitHub only allows PENDING deletion)
- GetAuthenticatedUser: returns login of the authed user
- RequestReviewer: add a user as requested reviewer

API types added: PullRequest, CommitStatus, ChangedFile, ReviewComment,
Review, ContentEntry.

Notable edge cases handled:
- GitHub embeds newlines in base64 content; stripped before decode
- GetFileContent returns error for non-file paths (type=dir)
- ListContents normalizes single-file response to a slice
- DeleteReview documents GitHub's PENDING-only constraint

Removes TODO comment from baseURL field (now consumed by all methods).

Closes part of #130.

Co-authored-by: Rodin <rodin@forgedthought.ai>

@@ -173,0 +175,4 @@
+	if vcsType == "" {
+		// Heuristic: if the URL looks like github.com or a GitHub Enterprise host,
+		// default to GitHub. The composite action sets VCS_TYPE explicitly, so this
+		// is a fallback for manual invocations.

@@ -0,0 +21,4 @@
+
+// ErrNotSupported is returned by VCS methods that have no implementation for
+// a particular VCS backend (e.g., Gitea-specific timeline APIs on GitHub).
+var ErrNotSupported = errors.New("operation not supported on this VCS backend")

@@ -0,0 +50,4 @@
+type giteaExtClient interface {
+	vcsClient
+	GetTimelineReviewCommentIDForReview(ctx context.Context, owner, repo string, prNum, reviewID int64) (int64, error)
+	EditComment(ctx context.Context, owner, repo string, commentID int64, body string) error

@@ -0,0 +295,4 @@
+func (a *githubVCSAdapter) ListContents(ctx context.Context, owner, repo, path string) ([]review.ContentEntry, error) {
+	entries, err := a.c.ListContents(ctx, owner, repo, path)
+	if err != nil {
+		return nil, err

@@ -379,0 +429,4 @@
+}
+
+// contentResponse is the GitHub contents API response for a single file.
+type contentResponse struct {

@@ -659,0 +814,4 @@
+		w.Write([]byte(`{"name":"README.md","path":"README.md","type":"file","content":"` + encoded + `","encoding":"base64"}`))
+	}))
+	defer srv.Close()
+

@@ -379,0 +427,4 @@
+	} `json:"user"`
+	State string `json:"state"`
+}
+

@@ -173,0 +175,4 @@
+	if vcsType == "" {
+		// Heuristic: if the URL looks like github.com or a GitHub Enterprise host,
+		// default to GitHub. The composite action sets VCS_TYPE explicitly, so this
+		// is a fallback for manual invocations.

@@ -0,0 +11,4 @@
+//     its respective client package's types.
+
+import (
+	"context"

@@ -0,0 +256,4 @@
+}
+
+func (a *githubVCSAdapter) GetPullRequestDiff(ctx context.Context, owner, repo string, number int) (string, error) {
+	return a.c.GetPullRequestDiff(ctx, owner, repo, number)

@@ -172,1 +173,3 @@
-	giteaClient := gitea.NewClient(*vcsURL, *reviewerToken)
+	// Detect VCS type: explicit flag > env var > URL heuristic (default: gitea).
+	vcsType := envOrDefault("VCS_TYPE", "")
+	if vcsType == "" {

@@ -0,0 +19,4 @@
+	"gitea.weiker.me/rodin/review-bot/review"
+)
+
+// ErrNotSupported is returned by VCS methods that have no implementation for

@@ -0,0 +84,4 @@
+// vcsReviewComment is an inline review comment.
+type vcsReviewComment struct {
+	Path        string
+	NewPosition int64 // Gitea: absolute line; GitHub: diff hunk position

@@ -379,0 +614,4 @@
+			return "", fmt.Errorf("decode base64 content for %s: %w", filepath, err)
+		}
+		return string(decoded), nil
+	}

@@ -659,0 +772,4 @@
+		t.Fatalf("unexpected error: %v", err)
+	}
+	if len(files) != 101 {
+		t.Errorf("len(files) = %d, want 101", len(files))

@@ -654,6 +692,19 @@ func evaluateCIStatus(statuses []gitea.CommitStatus) (passed bool, details strin
 	return true, "all checks passed"