feat(config): add interactive config editor and GitLab PR support (#4)

Revamp the configuration UI with an interactive editor that supports inline text editing, navigation, and field validation, replacing the previous sequential prompts. Add GitLab pull request creation support via the `glab` CLI, and extend back navigation to all interactive menus for a consistent user experience.

Reviewed-on: #4

test/pr.test.ts

@@ -0,0 +1,19 @@
+import { test, expect, describe } from "bun:test";
+import { detectPlatformFromHostname } from "../src/pr";
+
+describe("pr platform detection", () => {
+  test("detects supported hosted platforms", () => {
+    expect(detectPlatformFromHostname("github.com")).toBe("github");
+    expect(detectPlatformFromHostname("gitlab.com")).toBe("gitlab");
+  });
+
+  test("detects self-hosted platform hostnames", () => {
+    expect(detectPlatformFromHostname("gitlab.example.com")).toBe("gitlab");
+    expect(detectPlatformFromHostname("gitea.example.com")).toBe("gitea");
+  });
+
+  test("returns null for unknown hostnames", () => {
+    expect(detectPlatformFromHostname("git.example.com")).toBeNull();
+    expect(detectPlatformFromHostname(null)).toBeNull();
+  });
+});