types-and-values: add explanatory commentary to solution (#3067)

This commentary, written by Gemini, focuses on aspects of the solution
that differ from the baseline languages (C/Java/Python), highlighting
Rust-specific idioms and concepts.

Author: mgeisler

src/types-and-values/solution.md

@@ -4,6 +4,25 @@
 {{#include exercise.rs:solution}}
 ```
 
+We use the `return` syntax here to return values from the function. Later in the
+course, we will see that the last expression in a block is automatically
+returned, allowing us to omit the `return` keyword for a more concise style.
+
+The `if` condition `n < 2` does not need parentheses, which is standard Rust
+style.
+
+## Panic
+
+The exercise asks when this function will panic. The Fibonacci sequence grows
+very rapidly. With `u32`, the calculated values will overflow the 32-bit integer
+limit (4,294,967,295) when `n` reaches 48.
+
+In Rust, integer arithmetic checks for overflow in _debug mode_ (which is the
+default when using `cargo run`). If an overflow occurs, the program will panic
+(crash with an error message). In _release mode_ (`cargo run --release`),
+overflow checks are disabled by default, and the number will wrap around
+(modular arithmetic), producing incorrect results.
+
 <details>
 
 - Walk through the solution step-by-step.