feat: Improve the initial setup experience

- Issue a single-use token for initial account creation
- Disable registration through other methods until the first account is made
- Print helpful instructions to the console on the first run
- Improve the welcome message sent in the admin room on first run

src/service/Cargo.toml

@@ -79,6 +79,7 @@ zstd_compression = [
 ]
 
 [dependencies]
+askama.workspace = true
 async-trait.workspace = true
 base64.workspace = true
 bytes.workspace = true
@@ -118,6 +119,7 @@ webpage.optional = true
 blurhash.workspace = true
 blurhash.optional = true
 recaptcha-verify = { version = "0.1.5", default-features = false }
+yansi.workspace = true
 
 [target.'cfg(all(unix, target_os = "linux"))'.dependencies]
 sd-notify.workspace = true