feat: complete leetcode.cn support for problem list, detail, and id-based lookup

[dong-frank]

Background

This branch already supports basic site switching, but LeetCode CN uses a different schema from LeetCode Global for problem list and problem detail queries.
As a result, commands such as list, show, hint, pick had compatibility gaps under leetcode.cn.

This PR fills those gaps and ensures the command layer receives a normalized, consistent data model.

What Changed( Coding with Codex)

1. Added dedicated GraphQL queries for leetcode.cn (problem list and problem detail).
2. Added CN-specific Zod schema validation for list/detail responses.
3. Extended CN adapters to normalize list/detail payloads into the common internal model.
4. Updated client logic to handle CN-specific branches:
5. Problem list now uses CN query + CN schema + CN normalization.
6. Problem detail now uses CN query + CN schema + CN normalization.
7. ID-based lookup in CN now paginates list search by frontend ID, then fetches detail by slug.
8. Improved status normalization for CN-specific values (for example: tried, not_started).

And I tested

• npm run start -- list
• npm run start -- show 1
• npm run start -- hint 1
• npm run start -- pick 1
• npm run start Open the tui and successfully get the same problem list.