feat: automatically check and mark already solved questions

[Saarthak50]

Summary

This PR introduces a feature to dynamically identify and mark LeetCode questions that are already present in the user's linked GitHub repository. When visiting a problem page, the extension checks if the solution has already been pushed, and if so, styles the manual Push button as a green Pushed button.

How it works

1. Direct Path Check: The extension first checks for the default structured location of the problem's README.md (taking user settings like language or difficulty folder structures into account).
2. Search Fallback: If the folder is not found (status 404), it falls back to querying the GitHub Search API for the repository to search for files matching the problem slug, or camelCase/flat names (e.g. searching for "two-sum", filename:two-sum, or filename:twosum). This allows the extension to find solutions even if they are named differently (like TwoSum.java) or placed in custom paths.
3. Auto-Sync on Link: When linking an existing repository on the welcome page, it now automatically triggers a sync of solved counts.

Key Changes

src/js/leetcode.js

• LeetCodeV2.prototype.checkPushedStatus: Queries LeetCode GraphQL for question details, constructs the expected file path, checks if it exists in the GitHub repo, and falls back to a GitHub Code Search if it's not found in the default path.
• LeetCodeV2.prototype.getLanguage: Added fallback logic to retrieve the current language from the page's dropdown when submissionData is null (on page load).
• LeetCodeV2.prototype.addManualSubmitButton: Calls checkPushedStatus on page load to style the button as green and labeled Pushed if the solution is found.
• LeetCodeV2.prototype.markUploaded: Transitions the manual push button state to Pushed and turns it green immediately upon a successful manual push.
• getGitIcon: Changed hardcoded SVG fill color from #100f0d to currentColor so the icon adapts to the button text color (turns green when pushed).

src/js/welcome.js

• linkRepo: Programmatically triggers the Sync counts click event upon linking an existing repository to automatically sync counts.

Verification Done

• Formatted with Prettier (npm run format).
• Verified with ESLint (npx eslint src/js/leetcode.js src/js/welcome.js).
• Manually tested by linking repositories with both default folder structures and flat files (e.g. TwoSum.java), verifying that both are recognized and styled as Pushed on page load.