use url instead of localstorage

[martincai8]

Ticket: https://www.notion.so/nwplus/Investigate-localstorage-overwrite-14e14d529faa809f8043f9717d4e0b20

Description

• nuked localstorage in favour of reading the state from the url to create an independent single source of truth (solves the issue of localstorage values persisting through different tabs)
• simplified activeHackathon and dbHackathonName to be derived values instead of managed states

The idea is that whenever the url changes:

• useLocation() triggers a re-render of HackathonProvider
• urlHackathon is recalculated from the new URL
• activeHackathon gets derived from urlHackathon and dbHackathonName is derived from activeHackathon

Testing

• navigate through different pages, change the url, etc.
• testing the workflow that made things glitchy:
  • fill out an application for hackcamp
  • go to the dev firebase db and give yourself a status of acceptedAndAttending
  • delete your applicant object from nwHacks2025/Applicants if you already have an existing application
  • from the application page (/app/hackcamp/application), navigate to app/nwhacks/application/part-1 by changing the url manually
  • check the nwHacks2025/Applicants collection to see if you have a new blank object (previously, your application from hackcamp would be copied over)

[github-actions]

Visit the preview URL for this PR (updated for commit 88014b2):

https://nwplus-ubc--pr651-martin-bye-localstor-qqvhynxq.web.app

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