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/layout/justify.rs

@@ -0,0 +1,63 @@
+use crate::config::JustifyMode;
+use crate::format;
+use crate::layout::ActiveSection;
+
+/// Distribute extra space evenly across gaps between sections.
+/// Center the separator core (e.g., `|` from ` | `) within each gap.
+/// Remainder chars distributed left-to-right.
+pub fn justify(
+    active: &[ActiveSection],
+    term_width: u16,
+    separator: &str,
+    _mode: JustifyMode,
+) -> String {
+    let content_width: usize = active
+        .iter()
+        .map(|s| format::display_width(&s.output.raw))
+        .sum();
+
+    let num_gaps = active.len().saturating_sub(1);
+    if num_gaps == 0 {
+        return active
+            .first()
+            .map(|s| s.output.ansi.clone())
+            .unwrap_or_default();
+    }
+
+    let available = (term_width as usize).saturating_sub(content_width);
+    let gap_width = available / num_gaps;
+    let gap_remainder = available % num_gaps;
+
+    // Extract separator core (non-space chars, e.g. "|" from " | ")
+    let sep_core = separator.trim();
+    let sep_core_len = format::display_width(sep_core);
+
+    let mut output = String::new();
+    for (i, sec) in active.iter().enumerate() {
+        if i > 0 {
+            let this_gap = gap_width + usize::from(i - 1 < gap_remainder);
+            let gap_str = build_gap(sep_core, sep_core_len, this_gap);
+            output.push_str(&format!(
+                "{}{gap_str}{}",
+                crate::color::DIM,
+                crate::color::RESET
+            ));
+        }
+        output.push_str(&sec.output.ansi);
+    }
+
+    output
+}
+
+/// Center the separator core within a gap of `total` columns.
+fn build_gap(core: &str, core_len: usize, total: usize) -> String {
+    if core.is_empty() || core_len == 0 {
+        return " ".repeat(total);
+    }
+
+    let pad_total = total.saturating_sub(core_len);
+    let pad_left = pad_total / 2;
+    let pad_right = pad_total - pad_left;
+
+    format!("{}{core}{}", " ".repeat(pad_left), " ".repeat(pad_right))
+}