Migrate from Remix to React Router 7

[benvinegar]

I'm normally not in favor of aggressive upgrading of dependencies like this, but I do want to start exploring migrating the project back to a single Cloudflare Worker (#134), and before doing that wanted to make sure I was working from the "latest" way of doing things.

[codecov]

Codecov Report

Attention: Patch coverage is 47.05882% with 18 lines in your changes missing coverage. Please review.

Project coverage is 87.00%. Comparing base (1c544cd) to head (364cdf4).
Report is 6 commits behind head on main.

Files with missing lines	Patch %	Lines
packages/server/functions/collect.ts	0.00%	9 Missing ⚠️
packages/server/app/entry.client.tsx	0.00%	2 Missing ⚠️
packages/server/app/entry.server.tsx	0.00%	2 Missing ⚠️
packages/server/app/load-context.ts	0.00%	0 Missing and 1 partial ⚠️
packages/server/app/routes.ts	0.00%	0 Missing and 1 partial ⚠️
packages/server/app/routes/admin-redirect.tsx	0.00%	0 Missing and 1 partial ⚠️
packages/server/app/routes/collect.tsx	0.00%	0 Missing and 1 partial ⚠️
packages/server/functions/[[page]].ts	0.00%	0 Missing and 1 partial ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #146      +/-   ##
==========================================
- Coverage   87.26%   87.00%   -0.27%     
==========================================
  Files          38       38              
  Lines        2426     2439      +13     
  Branches      301      302       +1     
==========================================
+ Hits         2117     2122       +5     
- Misses        301      309       +8     
  Partials        8        8              

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