feat: multi-repo patterns + directory recursion

patterns-repo now accepts a comma-separated list of repos:
  PATTERNS_REPO="rodin/elixir-patterns,rodin/phoenix-conventions"

patterns-files accepts files AND directories:
  PATTERNS_FILES="README.md,docs/"

When a path is a directory, all files within it are fetched
recursively via the Gitea contents API. Only .md, .txt, .yml,
and .yaml files are included as pattern content.

New API methods:
- ListContents: list files/dirs at a path via contents API
- GetAllFilesInPath: recursively fetch all file contents

This allows a single review action to pull idioms from multiple
pattern repos (e.g. elixir-patterns + phoenix-conventions) and
include entire directories of documentation as review criteria.

gitea/client.go

@@ -177,3 +177,63 @@ func (c *Client) doGet(url string) ([]byte, error) {
 	}
 	return io.ReadAll(resp.Body)
 }
+
+// ContentEntry represents a file or directory entry from the contents API.
+type ContentEntry struct {
+	Name string `json:"name"`
+	Path string `json:"path"`
+	Type string `json:"type"` // "file" or "dir"
+}
+
+// ListContents lists files and directories at a given path in a repo.
+func (c *Client) ListContents(owner, repo, path string) ([]ContentEntry, error) {
+	url := fmt.Sprintf("%s/api/v1/repos/%s/%s/contents/%s", c.BaseURL, owner, repo, path)
+	body, err := c.doGet(url)
+	if err != nil {
+		return nil, fmt.Errorf("list contents %s: %w", path, err)
+	}
+	var entries []ContentEntry
+	if err := json.Unmarshal(body, &entries); err != nil {
+		return nil, fmt.Errorf("parse contents JSON: %w", err)
+	}
+	return entries, nil
+}
+
+// GetAllFilesInPath recursively fetches all file contents under a path.
+// If the path is a file, returns just that file's content.
+// If the path is a directory, recursively fetches all files within it.
+func (c *Client) GetAllFilesInPath(owner, repo, path string) (map[string]string, error) {
+	results := make(map[string]string)
+
+	// Try listing as directory first
+	entries, err := c.ListContents(owner, repo, path)
+	if err != nil {
+		// Might be a file, try fetching directly
+		content, fileErr := c.GetFileContent(owner, repo, path)
+		if fileErr != nil {
+			return nil, fmt.Errorf("path %q is neither a file nor directory: %w", path, err)
+		}
+		results[path] = content
+		return results, nil
+	}
+
+	for _, entry := range entries {
+		switch entry.Type {
+		case "file":
+			content, err := c.GetFileContent(owner, repo, entry.Path)
+			if err != nil {
+				continue // Skip files we can't read
+			}
+			results[entry.Path] = content
+		case "dir":
+			subResults, err := c.GetAllFilesInPath(owner, repo, entry.Path)
+			if err != nil {
+				continue
+			}
+			for k, v := range subResults {
+				results[k] = v
+			}
+		}
+	}
+	return results, nil
+}