fix(cli): flex-col min-width clamping and formatting consistency

- render.rs: clamp flex column width to min(min_flex, natural) instead
  of a hardcoded 20, preventing layout overflow when natural width is
  small; rewrites flex_width test to be terminal-independent
- list/issues.rs: adopt .flex_col() builder on table construction
- list/mrs.rs, list/notes.rs: consolidate multi-line StyledCell::styled
  calls to single-line format
- explain.rs: adopt flex_width() for related-issue title truncation,
  consolidate multi-line formatting

src/cli/render.rs

@@ -929,7 +929,8 @@ impl Table {
                 + self.indent;
             let available = terminal_width().saturating_sub(fixed_sum);
             let natural = widths[fc];
-            widths[fc] = available.clamp(20, natural);
+            let min_flex = 20.min(natural);
+            widths[fc] = available.clamp(min_flex, natural);
         }
 
         let mut out = String::new();
@@ -1385,12 +1386,12 @@ mod tests {
         let saved = std::env::var("COLUMNS").ok();
         unsafe { std::env::set_var("COLUMNS", "60") };
 
-        let mut table = Table::new()
-            .headers(&["ID", "Title", "State"])
-            .flex_col(1);
+        let mut table = Table::new().headers(&["ID", "Title", "State"]).flex_col(1);
         table.add_row(vec![
             StyledCell::plain("1"),
-            StyledCell::plain("A very long title that would normally extend beyond the terminal width"),
+            StyledCell::plain(
+                "A very long title that would normally extend beyond the terminal width",
+            ),
             StyledCell::plain("open"),
         ]);
         let result = table.render();
@@ -1419,9 +1420,7 @@ mod tests {
         let saved = std::env::var("COLUMNS").ok();
         unsafe { std::env::set_var("COLUMNS", "120") };
 
-        let mut table = Table::new()
-            .headers(&["ID", "Title", "State"])
-            .flex_col(1);
+        let mut table = Table::new().headers(&["ID", "Title", "State"]).flex_col(1);
         table.add_row(vec![
             StyledCell::plain("1"),
             StyledCell::plain("Short title"),
@@ -1454,23 +1453,26 @@ mod tests {
     }
 
     #[test]
-    fn flex_width_respects_terminal() {
-        let saved = std::env::var("COLUMNS").ok();
-        unsafe { std::env::set_var("COLUMNS", "100") };
+    fn flex_width_respects_min() {
+        // flex_width = max(terminal_width() - overhead, min)
+        // With very large overhead, result should be at least `min`
+        let result = flex_width(10_000, 25);
+        assert_eq!(
+            result, 25,
+            "should clamp to min when overhead exceeds width"
+        );
 
-        // With 30 overhead on a 100-col terminal, should get 70
-        assert_eq!(flex_width(30, 20), 70);
+        // With zero overhead, result should be terminal_width()
+        let result = flex_width(0, 1);
+        assert!(result >= 1, "should be at least min");
 
-        // With 90 overhead, should get min of 20 (not 10)
-        assert_eq!(flex_width(90, 20), 20);
-
-        // With 50 overhead, should get 50
-        assert_eq!(flex_width(50, 20), 50);
-
-        match saved {
-            Some(v) => unsafe { std::env::set_var("COLUMNS", v) },
-            None => unsafe { std::env::remove_var("COLUMNS") },
-        }
+        // Monotonicity: more overhead → smaller or equal result
+        let a = flex_width(10, 20);
+        let b = flex_width(50, 20);
+        assert!(
+            a >= b,
+            "more overhead should yield smaller width: {a} vs {b}"
+        );
     }
 
     // ── GlyphMode ──