Fix remaining CODEGEN math rendering: split all multi-line $$ blocks

8 display math blocks had $$ on the same line as the opening content
(e.g., $$0 = \begin{cases}). Split them so $$ is always on its own
line for remark-math compatibility.

Author: apetros

src/content/docs/developer/codegen-library.mdx

@@ -1090,7 +1090,8 @@ $z \in \{-1, 0, 1\}$
 
 #### Equations
 
-$$0 = \begin{cases}
+$$
+0 = \begin{cases}
 \dot{x}_i = K_i x_k & \text{if } z = 0 \\
 x_i - x_i^{min} & \text{if } z = -1 \\
 x_i - x_i^{max} & \text{if } z = 1
@@ -1246,15 +1247,17 @@ $z \in \{-2, -1, 0, 1, 2\}$
 
 #### Equations
 
-$$\text{if } z = 0: \quad
+$$
+\text{if } z = 0: \quad
 \begin{cases}
 0 = K_p x_k + x_1 - x_j \\
 \dot{x}_1 = K_i \, x_k \\
 0 = x_2 - x_1
 \end{cases}
 $$
 
-$$\text{if } z = 2: \quad
+$$
+\text{if } z = 2: \quad
 \begin{cases}
 0 = x_j^{max} - x_j \\
 \dot{x}_1 = 0 \\
@@ -1269,7 +1272,8 @@ $$\text{if } z = 2: \quad
 \end{cases}
 $$
 
-$$\text{if } z = -2: \quad
+$$
+\text{if } z = -2: \quad
 \begin{cases}
 0 = x_j^{min} - x_j \\
 \dot{x}_1 = 0 \\
@@ -1823,7 +1827,8 @@ $z \in \{1, 2\}$
 
 #### Equations
 
-$$0 = \begin{cases}
+$$
+0 = \begin{cases}
 x_l - x_i & \text{if } z = 1 \\
 x_l - x_j & \text{if } z = 2
 \end{cases}
@@ -1877,7 +1882,8 @@ $z \in \{-1, 0, 1\}$
 
 #### Equations
 
-$$0 = \begin{cases}
+$$
+0 = \begin{cases}
 x_j & \text{if } z \in \{-1, 0\} \\
 x_j - 1 & \text{if } z = 1
 \end{cases}
@@ -1943,7 +1949,8 @@ $z \in \{-1, 0, 1\}$
 
 #### Equations
 
-$$0 = \begin{cases}
+$$
+0 = \begin{cases}
 x_j & \text{if } z \in \{-1, 0\} \\
 x_j - 1 & \text{if } z = 1
 \end{cases}
@@ -2008,7 +2015,8 @@ $z \in \{1, 2\}$ represents the automaton state.
 
 #### Equations
 
-$$0 = \begin{cases}
+$$
+0 = \begin{cases}
 x_k - v_1 & \text{if } z = 1 \\
 x_k - v_2 & \text{if } z = 2
 \end{cases}