Added Feat-interactive widgets

[Kishalll]

fixes #43

feat: community widgets + full-page post view

Added real data to community sidebar widgets and opened posts in a dedicated full-screen page instead of
inline expansion.

Community widgets (bac36d8)

• Weekly challenge widget fetches from /api/community/weekly-challenge via a new WeeklyChallengeStore
  bean — serves title, difficulty, days left, and a link
• Community stats widget pulls live postsToday and top 3 contributors by post count from a new
  /api/community/stats endpoint
• Added fetchWeeklyChallenge and fetchCommunityStats to the API service
• Added /auth/demo-login — creates a demo account on first call and returns a JWT cookie, useful for
  testing without a real signup

Full-page post view (fcf4fb7)

• Clicking a post navigates to /community/post/:id instead of expanding inline
• New PostPage renders full markdown content with the same Sidebar + Topbar shell, upvote, and save
  actions
• Removed all inline expand / dim logic from CommunityPage

[vercel]

@Kishalll is attempting to deploy a commit to the ashishkaranam06-9122's projects Team on Vercel.

A member of the Team first needs to authorize it.

[Kishalll]

@ashish-066 pls review

[Kishalll]

@ashish-066 i also found lot of issue in this project currently , and i'd be happy to raise issues and fix them under gssoc if the proj is active

[ashish-066]

@Kishalll please do raise them

[Kishalll]

okay @ashish-066 , pls review this pr

[Kishalll]

@ashish-066 pls review