feat(gitea): add domain model classes, helpers, and refactor GiteaClient internals; expand README with usage and docs

ts/gitea.classes.branch.ts

@@ -0,0 +1,18 @@
+import type { IGiteaBranch } from './gitea.interfaces.js';
+
+export class GiteaBranch {
+  public readonly name: string;
+  public readonly commitSha: string;
+
+  constructor(raw: IGiteaBranch) {
+    this.name = raw.name || '';
+    this.commitSha = raw.commit?.id || '';
+  }
+
+  toJSON(): IGiteaBranch {
+    return {
+      name: this.name,
+      commit: { id: this.commitSha },
+    };
+  }
+}