fix(dsl): render each margin on its own line

Each [m] block occupies its own line in the article. Blank paragraphs
and whitespace-only lines are dropped.

app/src/main/java/com/example/research/ui/article/DslAnnotatedParser.kt

@@ -91,6 +91,7 @@ object DslAnnotatedParser {
         var accentNext = false
         var currentIndent = 0
         var mClosedPendingBreak = false
+        var lastAppended: Char? = null
         val exampleStyle = SpanStyle(color = colorScheme.secondaryText)
         val labelStyle = SpanStyle(color = colorScheme.labelText)
         val linkStyle = SpanStyle(color = colorScheme.linkText, textDecoration = TextDecoration.Underline)
@@ -108,20 +109,23 @@ object DslAnnotatedParser {
         }
 
         fun flushBlock() {
-            if (builder.length > 0) {
+            val text = builder.toAnnotatedString()
+            if (text.any { !it.isWhitespace() }) {
                 result.add(DslBlock(
-                    text = builder.toAnnotatedString(),
+                    text = text,
                     indent = currentIndent,
                     lazyRefs = lazyRefs.toList()
                 ))
+            }
             builder = AnnotatedString.Builder()
             stack.forEach { builder.pushStyle(it) }
             lazyRefs.clear()
-            }
+            lastAppended = null
             mClosedPendingBreak = false
         }
 
         fun appendChar(char: Char) {
+            lastAppended = char
             if (mClosedPendingBreak) {
                 mClosedPendingBreak = false
                 if (refStack.isEmpty() && !char.isWhitespace()) {
@@ -209,8 +213,8 @@ object DslAnnotatedParser {
                                     }
                                     "b" -> push(SpanStyle(fontWeight = FontWeight.Bold))
                                     "m", "m0", "m1", "m2", "m3", "m4", "m5" -> {
-                                        if (builder.length > 0) {
-                                            if (refStack.isEmpty()) flushBlock() else builder.append("\n")
+                                        if (lastAppended != null && !lastAppended!!.isWhitespace()) {
+                                            flushBlock()
                                         }
                                         currentIndent = marginIndent(tagName)
                                         push(exampleStyle)
@@ -243,6 +247,14 @@ object DslAnnotatedParser {
                     appendChar(char)
                     i++
                 }
+                '\n' -> {
+                    if (refStack.isEmpty()) {
+                        flushBlock()
+                    } else {
+                        appendChar(char)
+                    }
+                    i++
+                }
                 else -> {
                     appendChar(char)