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

README.md

@@ -22,7 +22,7 @@ Generate **Conventional Commits** messages and pull request descriptions using A
 - **Conventional Commits** — `feat(scope): description` format by default
 - **Interactive file selection** — ↑/↓ to navigate, space to select, top-level "Select all"
 - **Inline editing** — edit AI-generated messages right in the terminal with cursor movement
-- **AI-generated PRs** — create GitHub or Gitea pull requests with generated title and body
+- **AI-generated PRs** — create GitHub, Gitea, or GitLab pull requests with generated title and body
 - **OpenAI-compatible API** — works with DeepSeek, OpenAI, Ollama, OpenRouter, and more
 - **Review before commit** — confirm, edit, or abort the generated message
 - **Bun-native runtime** — built on Bun APIs with no runtime npm dependencies
@@ -84,7 +84,7 @@ $ gai commit
 
   Select files to stage:
   2 unstaged files available
-  ↑/↓ navigate · space toggle · enter confirm · ctrl+c cancel
+  ↑/↓ navigate · space toggle · enter confirm · ←/backspace back · ctrl+c cancel
 
   ❯ □ Select all
     □ src/ai.ts      modified
@@ -108,6 +108,7 @@ $ gai commit
 
 - GitHub remotes use the `gh` CLI
 - Gitea remotes use the `tea` CLI
+- GitLab remotes use the `glab` CLI
 - Unknown remotes prompt you to choose a platform
 
 The command compares your current branch against the default branch, pushes the branch if needed, generates a PR title/body from the branch commits and diff, then asks for confirmation before creating the PR.