fix(ui): Refactor and improve XHR for empathy and post deletion

[ashquarky]

Resolves #XXX

Changes:

Refactors how XHR is handled in the client JS. This was initially intended as a CTR fix for the Cloudflare XSS trip, but the error handling was improved enough to justify porting it to all platforms.

Thankfully, due to the bundler modernising CTR's syntax a lot, it's tolerable to just copy-paste the code between the three, with the only big issue being var/const.

• Finish setting up TypeScript for the client JS. This includes eslint rules and types for the browser globals.
• Pull XHR code out into a seperate TypeScript file and modernise it a little (onload works - it's old Chrome, not IE6!)
• Split empathy and delete API calls into their own functions, a bit reminiscent of the gRPC stuff on the server side. Also improve the error handling for JSON parse errors and others.
  • The delete API doesn't actually return a JSON object from the server - fake it for now, I'll change the server route to be more sensible later.
• Work around an issue on CTR where only GET and POST requests work. (This is probably related to Nintendo's domain allowlist on this platform)
  • This works with a HTTP header to override the method. Infra: does "smuggling" request methods have security implications, especially via Cloudflare? Can limit to CTR endpoints if it's a problem.
• Unify the post deletion experience across platforms, with the same texts and error messages.
• Fix a CSS bug where the toast on web appeared behind the navbar in mobile layout.

This touches the post templates to remove the onclick handlers, so #295 will need equivalent changes to the TSX versions.

The XHR and API files are near-identical between platforms, so a good candidate for a @repo/client-common library. Food for thought.

• I have read and agreed to the Code of Conduct.
• I have read and complied with the contributing guidelines.
• What I'm implementing was an approved issue.
• I have tested all of my changes.

[mrjvs]

Tested everything, looks like everything is working. Just a couple review comments.

Also TIL: You can't delete replies on 3ds

[mrjvs]

Code looks good, I'm waiting on the moderator team to give some feedback on the redirect changes before I approve

[mrjvs]

The mod team agreed with this approach, so this is good to merge I think

[ashquarky]

Waiting for #306

[mrjvs]

Waiting for #306

Segmentation fault (core dumped)
Process exited with exit code 139

[mrjvs]

(yes, I am approving my own commits now)