Internal improvements

[shalvah]

The goal here is to improve the development experience.

• Make it easier for existing devs (me) to add new features
• Make it easy for new devs to get started
• Make it easier to find and fix issues
• Make it easier to reproduce scenarios. For instance, how do you test that a Firebase notification works locally? How do you test one part of the application without going through Twitter?
• Make it easier to perform administrative tasks. For instance, if I need to manually force a reminders check.

Achieving these will include things like:

• Improving the README. The Implementation section may be out of date.
• Adding a development guide.
• Setting up better test mocks
• Setting up reliable local emulation environments
• Adding better instrumentation
• Fixing some existing issues logged by Sentry, such as issues with auth.
• Create runbooks for admin tasks and failure scenarios
• Reorganizing the code so it's easier to follow

This will be a long-term thing, so I may end up splitting this into multiple issues/PRs.

[shalvah]

Also:

• Capturing better contextual information in Sentry (such as user data) — it'll help debug issues better
• Moving from console.log-ging important info to attaching it to the trace.

[shalvah]

Might also look into tracking better metrics and possibly adding an /open page. Guess this is turning into more of a roadmap than a specific issue.😅