fix(docs): generate URL-safe Postgres passwords

openssl rand -base64 24 can emit URI-reserved characters (/, +, =). Since POSTGRES_PASSWORD is interpolated unescaped into DATABASE_URL, such a password breaks the connection URL and blocks boot. Switch every documented example to openssl rand -hex 32 (URL-safe, 256-bit).

docs/self-hosting/getting-started.md

@@ -38,7 +38,7 @@ HealthLog needs three secrets before it will boot. Generate them with
 `openssl` and append to `.env`:
 
 ```bash
-echo "POSTGRES_PASSWORD=$(openssl rand -base64 24)" >> .env
+echo "POSTGRES_PASSWORD=$(openssl rand -hex 32)" >> .env
 echo "ENCRYPTION_KEY=$(openssl rand -hex 32)"       >> .env
 echo "API_TOKEN_HMAC_KEY=$(openssl rand -hex 32)"   >> .env
 ```