feat(style): gate ANSI colour on tty detection

One wrapper per colour plus a padding helper, all no-ops when stdout is not a
terminal, so piped output and CI logs stay readable.

lib/style.ml

@@ -0,0 +1,39 @@
+let enabled = ref true
+
+let wrap code s = if !enabled then "\027[" ^ code ^ "m" ^ s ^ "\027[0m" else s
+
+let bold s = wrap "1" s
+let dim s = wrap "2" s
+let red s = wrap "31" s
+let green s = wrap "32" s
+let yellow s = wrap "33" s
+let blue s = wrap "34" s
+let magenta s = wrap "35" s
+let cyan s = wrap "36" s
+
+let visible s =
+  let n = String.length s in
+  let rec go i acc =
+    if i >= n then acc
+    else if s.[i] = '\027' then
+      let rec skip j = if j >= n || s.[j] = 'm' then j + 1 else skip (j + 1) in
+      go (skip i) acc
+    else go (i + 1) (acc + 1)
+  in
+  go 0 0
+
+let pad n s = s ^ String.make (max 0 (n - visible s)) ' '
+
+let pad_left n s = String.make (max 0 (n - visible s)) ' ' ^ s
+let ellipsis n s = if visible s <= n then s else String.sub s 0 (max 0 (n - 1)) ^ "\xe2\x80\xa6"
+let plural n w =
+  let last = if w = "" then ' ' else w.[String.length w - 1] in
+  let prev = if String.length w < 2 then ' ' else w.[String.length w - 2] in
+  let form =
+    if n = 1 then w
+    else if last = 'y' && not (List.mem prev [ 'a'; 'e'; 'i'; 'o'; 'u' ]) then
+      String.sub w 0 (String.length w - 1) ^ "ies"
+    else if List.mem last [ 's'; 'x'; 'z' ] then w ^ "es"
+    else w ^ "s"
+  in
+  Printf.sprintf "%d %s" n form