feat: complete Rust port of claude-statusline

Port the entire 2236-line bash statusline script to Rust.
Implements all 25 sections, 3-phase layout engine (render, priority
drop, flex/justify), file-based caching with flock, 9-level terminal
width detection, trend sparklines, and deep-merge JSON config.

Release binary: 864K with LTO. Render time: <1ms warm.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

src/color.rs

@@ -0,0 +1,76 @@
+use crate::config::ThemeColors;
+use crate::theme::Theme;
+
+pub const RESET: &str = "\x1b[0m";
+pub const BOLD: &str = "\x1b[1m";
+pub const DIM: &str = "\x1b[2m";
+pub const RED: &str = "\x1b[31m";
+pub const GREEN: &str = "\x1b[32m";
+pub const YELLOW: &str = "\x1b[33m";
+pub const BLUE: &str = "\x1b[34m";
+pub const MAGENTA: &str = "\x1b[35m";
+pub const CYAN: &str = "\x1b[36m";
+pub const WHITE: &str = "\x1b[37m";
+
+/// Resolve a color name to ANSI escape sequence(s).
+pub fn resolve_color(name: &str, theme: Theme, palette: &ThemeColors) -> String {
+    if let Some(key) = name.strip_prefix("p:") {
+        let map = match theme {
+            Theme::Dark => &palette.dark,
+            Theme::Light => &palette.light,
+        };
+        if let Some(resolved) = map.get(key) {
+            return resolve_color(resolved, theme, palette);
+        }
+        return RESET.to_string();
+    }
+
+    let mut result = String::new();
+    for part in name.split_whitespace() {
+        result.push_str(match part {
+            "red" => RED,
+            "green" => GREEN,
+            "yellow" => YELLOW,
+            "blue" => BLUE,
+            "magenta" => MAGENTA,
+            "cyan" => CYAN,
+            "white" => WHITE,
+            "dim" => DIM,
+            "bold" => BOLD,
+            _ => "",
+        });
+    }
+
+    if result.is_empty() {
+        RESET.to_string()
+    } else {
+        result
+    }
+}
+
+/// Determine whether color output should be used.
+pub fn should_use_color(cli_color: Option<&str>, config_color: &crate::config::ColorMode) -> bool {
+    if std::env::var("NO_COLOR").is_ok() {
+        return false;
+    }
+
+    if let Some(flag) = cli_color {
+        return match flag {
+            "always" => true,
+            "never" => false,
+            _ => atty_stdout(),
+        };
+    }
+
+    match config_color {
+        crate::config::ColorMode::Always => true,
+        crate::config::ColorMode::Never => false,
+        crate::config::ColorMode::Auto => {
+            atty_stdout() && std::env::var("TERM").map_or(true, |t| t != "dumb")
+        }
+    }
+}
+
+fn atty_stdout() -> bool {
+    unsafe { libc::isatty(libc::STDOUT_FILENO) != 0 }
+}