feat: neofetch-style system info dump at startup

Prints DORF SYSTEM box to stdout before game loop begins:
OS, CPU (model + cores), GPU (WEBGPU_ADAPTER_NAME env var),
RAM total + free (from /proc/meminfo), display vsync mode,
initial chunk radius, world seed.

src/system_info.rs

@@ -0,0 +1,118 @@
+use std::env;
+use std::fs;
+
+use crate::config::{GameConfig, VsyncMode};
+use crate::constants::SEED;
+
+pub fn print_system_info(config: &GameConfig) {
+    let os = format!("{} {}", env::consts::OS, env::consts::ARCH);
+    let cpu = cpu_info();
+    let gpu = gpu_info();
+    let (ram_total, ram_free) = mem_info();
+    let display = vsync_label(&config.display.vsync);
+    let radius = config.initial_chunk_radius;
+    let seed = SEED;
+
+    let line_width = 34;
+    let hline = format!("{:─<width$}", "", width = line_width);
+
+    println!();
+    println!("╔═{hline}═╗");
+    println!("║{:^width$}║", "DORF SYSTEM", width = line_width + 2);
+    println!("╠═{hline}═╣");
+    println!("║  OS:      {:<width$}║", os, width = line_width);
+    println!("║  CPU:     {:<width$}║", cpu, width = line_width);
+    println!("║  GPU:     {:<width$}║", gpu, width = line_width);
+    println!(
+        "║  RAM:     {:<width$}║",
+        format!("{} GB ({} GB free)", ram_total, ram_free),
+        width = line_width
+    );
+    println!("║  Display: {:<width$}║", display, width = line_width);
+    println!(
+        "║  Radius:  {:<width$}║",
+        format!("{} chunks", radius),
+        width = line_width
+    );
+    println!("║  Seed:    {:<width$}║", seed, width = line_width);
+    println!("╚═{hline}═╝");
+    println!();
+}
+
+fn cpu_info() -> String {
+    #[cfg(target_os = "linux")]
+    {
+        let Ok(content) = fs::read_to_string("/proc/cpuinfo") else {
+            return String::from("Unknown CPU");
+        };
+
+        let model_name = content
+            .lines()
+            .find(|l| l.starts_with("model name"))
+            .and_then(|l| l.split(':').nth(1))
+            .map(|s| s.trim().to_string())
+            .unwrap_or_else(|| String::from("Unknown CPU"));
+
+        let core_count = content
+            .lines()
+            .filter(|l| l.starts_with("processor"))
+            .count()
+            .max(1);
+
+        format!("{} ({} cores)", model_name, core_count)
+    }
+
+    #[cfg(not(target_os = "linux"))]
+    {
+        let cores = env::var("NUMBER_OF_PROCESSORS")
+            .ok()
+            .and_then(|s| s.parse::<usize>().ok())
+            .unwrap_or(1);
+
+        format!("Unknown CPU ({} cores)", cores)
+    }
+}
+
+fn gpu_info() -> String {
+    env::var("WEBGPU_ADAPTER_NAME").unwrap_or_else(|_| String::from("Unknown GPU"))
+}
+
+fn mem_info() -> (u64, u64) {
+    #[cfg(target_os = "linux")]
+    {
+        let Ok(content) = fs::read_to_string("/proc/meminfo") else {
+            return (0, 0);
+        };
+
+        let parse_kb = |key: &str| -> u64 {
+            content
+                .lines()
+                .find(|l| l.starts_with(key))
+                .and_then(|l| {
+                    l.split_whitespace()
+                        .nth(1)
+                        .and_then(|s| s.parse::<u64>().ok())
+                })
+                .unwrap_or(0)
+        };
+
+        let total_kb = parse_kb("MemTotal:");
+        let available_kb = parse_kb("MemAvailable:");
+        let total_gb = total_kb / 1024 / 1024;
+        let available_gb = available_kb / 1024 / 1024;
+        (total_gb, available_gb)
+    }
+
+    #[cfg(not(target_os = "linux"))]
+    {
+        (0, 0)
+    }
+}
+
+fn vsync_label(mode: &VsyncMode) -> &'static str {
+    match mode {
+        VsyncMode::Vsync => "vsync",
+        VsyncMode::Mailbox => "mailbox vsync",
+        VsyncMode::Uncapped => "uncapped",
+    }
+}