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_test.go

@@ -2,6 +2,7 @@ package gitea
 
 import (
 	"encoding/json"
+	"fmt"
 	"net/http"
 	"net/http/httptest"
 	"testing"
@@ -238,3 +239,57 @@ func TestGetFileContentRef(t *testing.T) {
 		t.Errorf("unexpected content: %q", content)
 	}
 }
+
+func TestListContents(t *testing.T) {
+	server := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		if r.URL.Path != "/api/v1/repos/owner/repo/contents/docs" {
+			t.Errorf("unexpected path: %s", r.URL.Path)
+		}
+		w.Header().Set("Content-Type", "application/json")
+		fmt.Fprintf(w, `[{"name":"guide.md","path":"docs/guide.md","type":"file"},{"name":"sub","path":"docs/sub","type":"dir"}]`)
+	}))
+	defer server.Close()
+
+	client := NewClient(server.URL, "test-token")
+	entries, err := client.ListContents("owner", "repo", "docs")
+	if err != nil {
+		t.Fatalf("unexpected error: %v", err)
+	}
+	if len(entries) != 2 {
+		t.Fatalf("expected 2 entries, got %d", len(entries))
+	}
+	if entries[0].Type != "file" || entries[0].Path != "docs/guide.md" {
+		t.Errorf("unexpected first entry: %+v", entries[0])
+	}
+	if entries[1].Type != "dir" {
+		t.Errorf("expected dir type, got %s", entries[1].Type)
+	}
+}
+
+func TestGetAllFilesInPath_File(t *testing.T) {
+	server := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		if r.URL.Path == "/api/v1/repos/owner/repo/contents/README.md" {
+			// Gitea returns 404 for contents API on files (it's not a dir)
+			http.NotFound(w, r)
+			return
+		}
+		if r.URL.Path == "/api/v1/repos/owner/repo/raw/README.md" {
+			fmt.Fprintf(w, "# Hello")
+			return
+		}
+		http.NotFound(w, r)
+	}))
+	defer server.Close()
+
+	client := NewClient(server.URL, "test-token")
+	files, err := client.GetAllFilesInPath("owner", "repo", "README.md")
+	if err != nil {
+		t.Fatalf("unexpected error: %v", err)
+	}
+	if len(files) != 1 {
+		t.Fatalf("expected 1 file, got %d", len(files))
+	}
+	if files["README.md"] != "# Hello" {
+		t.Errorf("unexpected content: %q", files["README.md"])
+	}
+}