src/pages: add ChallengeInactivePage to show when no active challenge

[maceksimon]

Add ChallengeInactivePage and define states "challenge active" and "challenge inactive".

New page:

• 📄 Add new page ChallengeInactivePage.
• 🧩 Add new component ChallengeInactiveInfo displaying info text.
• 🌒 Add dark variant to ListCardPost so we can reuse it on the ChallengeInactivePage.
• 🔘 Update button "All posts" in ListCardPost - linking to RTWBB blog.
• 🧩 Add new component SocialBar for displaying links to social media on ChallengeInactivePage.
• 🔧 Refactor the social links data into a fixture and add logic to build array in useSocialLinks composable.

New states:

• 📦 Update challenge store with a getter for the isActiveChallenge state.
• 🔀 Update router rules adding the isActiveChallenge state condition.
• ✅ Update tests and add new tests for active and inactive states.
• 🔧 In commonTests, add functions encapsulating common intercept sets for active and inactive states.
• 📝 Add thisChallenge fixture with phase sets showing the challenge state.
• 📝 Add fixtures to simulate logging in in different states. Includes renaming systemTime variables for different purposes:
  • systemTimeLoggedIn- testing logging in with a token (originally systemTime).
  • systemTimeChallengeActive + systemTimeChallengeInactive - testing challenge state.