test: add Phase104 json_cur read_digits fixture and smokes

apps/tests/phase104_read_digits_json_cur_min.hako

@@ -0,0 +1,25 @@
+// Phase 104 (P2): real-app derived fixture from apps/libs/json_cur.hako:read_digits_from
+// Expect numeric output lines: 2 then 1
+
+static box Main {
+  read_digits_from(s, pos) {
+    local out = ""
+    local i = pos
+    if i < 0 { return out }
+
+    loop (true) {
+      local ch = s.substring(i, i+1)
+      if ch == "" { break }
+      if ch == "0" || ch == "1" || ch == "2" || ch == "3" || ch == "4" || ch == "5" || ch == "6" || ch == "7" || ch == "8" || ch == "9" { out = out + ch  i = i + 1 } else { break }
+    }
+    return out
+  }
+
+  main() {
+    local a = read_digits_from("12x", 0)
+    local b = read_digits_from("9", 0)
+    print(a.length())
+    print(b.length())
+    return "OK"
+  }
+}