End-to-end tests for core flows

[th0rgall]

We have Playwright set up for our project now, as well as a local Firebase emulators development environment that can be automated.

The following sequential e2e test flow would be extremely valuable:

**User 1:**

1. Create account
2. Verify account
3. Add garden
4. Log out

**User 2**
1. Create account
2. Verify account
3. On the map, click the garden of User 1
4. Ask to chat with User 1
6. Send a message to User 1

**User 1**
1. Log back in
1. Go to chat pane 
2. Read incoming chat

This verifies, both on the frontend and backend:

• that people can create accounts
• that they can create a garden
• that they can send a message to another garden
• and that that message can be read.

which is the core of WTMG!

It would be good to have this run as part of CI too.

[th0rgall]

We could also look into https://www.cypress.io/app/#browser_testing for this.