[chore] Refactor settings panel routing (and other fixes)

[tsmethurst]

Description

If this is a code change, please include a summary of what you've coded, and link to the issue(s) it closes/implements.

If this is a documentation change, please briefly describe what you've changed and why.

Mind-boggling refactor of our settings panel routing and menu stuff

• Separate routing and menu building into submodules and make it so typescript works with them properly.
• Removes some dependencies we were hardly using or not using.
• Use latest version of wouter, and tidy up code issues that came from the upgrade (particularly round the Link component).
• Type some more stuff.
• Fix some small HTML errors (<a>s embedded inside <a>s, <p>s embedded inside <p>s, things like that).

Checklist

Please put an x inside each checkbox to indicate that you've read and followed it: [ ] -> [x]

If this is a documentation change, only the first checkbox must be filled (you can delete the others if you want).

• I/we have read the GoToSocial contribution guidelines.
• I/we have discussed the proposed changes already, either in an issue on the repository, or in the Matrix chat.
• I/we have not leveraged AI to create the proposed changes.
• I/we have performed a self-review of added code.
• I/we have written code that is legible and maintainable by others. <-- hope so, that was the idea
• I/we have commented the added code, particularly in hard-to-understand areas.
• I/we have made any necessary changes to documentation.
• I/we have added tests that cover new code.
• I/we have run tests and they pass locally with the changes.
• I/we have run go fmt ./... and golangci-lint run.