fix: 3 bugs from peer code review

- justify: gate DIM/RESET separator coloring on color_enabled param;
  previously leaked ANSI escapes when --color=never or NO_COLOR was set
- vcs: apply branch name truncation per config (truncate.enabled,
  truncate.max, truncate.style) for both git and jj renderers;
  previously ignored truncate config causing long branch names to
  overflow and trigger unnecessary priority drops
- flex: account for prefix/suffix overhead when computing context_bar
  flex expansion width; previously double-applied apply_formatting
  causing line to overshoot term_width when prefix/suffix configured

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

src/layout/justify.rs

@@ -10,6 +10,7 @@ pub fn justify(
     term_width: u16,
     separator: &str,
     _mode: JustifyMode,
+    color_enabled: bool,
 ) -> String {
     let content_width: usize = active
         .iter()
@@ -37,11 +38,15 @@ pub fn justify(
         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
-            ));
+            if color_enabled {
+                output.push_str(&format!(
+                    "{}{gap_str}{}",
+                    crate::color::DIM,
+                    crate::color::RESET
+                ));
+            } else {
+                output.push_str(&gap_str);
+            }
         }
         output.push_str(&sec.output.ansi);
     }