feat: support rich multi-paragraph notes with formatting (Closes #7)

Add {start_of_notes}/{end_of_notes} (and short forms {son}/{eon}) block
directives to ChordProParser for multi-paragraph note content. Blank lines
within the block separate paragraphs. The renderer now word-wraps note
paragraphs to fit within the content width. MeasurementEngine estimates
wrapped line count for more accurate height calculations.

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

layout/src/main/kotlin/de/pfadfinder/songbook/layout/MeasurementEngine.kt

@@ -58,11 +58,23 @@ class MeasurementEngine(
             heightMm += config.layout.verseSpacing
         }
 
-        // Notes at bottom
+        // Notes at bottom (with word-wrap estimation for multi-paragraph notes)
         if (song.notes.isNotEmpty()) {
-            heightMm += 1.5f  // gap
-            for (note in song.notes) {
-                heightMm += fontMetrics.measureLineHeight(config.fonts.metadata, config.fonts.metadata.size) * 1.5f
+            heightMm += 1.5f  // gap before notes
+            val metaLineHeight = fontMetrics.measureLineHeight(config.fonts.metadata, config.fonts.metadata.size) * 1.5f
+            // A5 content width in mm = 148 - inner margin - outer margin
+            val contentWidthMm = 148f - config.layout.margins.inner - config.layout.margins.outer
+
+            for ((idx, note) in song.notes.withIndex()) {
+                // Estimate how many wrapped lines this note paragraph needs
+                val noteWidthMm = fontMetrics.measureTextWidth(note, config.fonts.metadata, config.fonts.metadata.size)
+                val estimatedLines = maxOf(1, kotlin.math.ceil((noteWidthMm / contentWidthMm).toDouble()).toInt())
+                heightMm += metaLineHeight * estimatedLines
+
+                // Paragraph spacing between note paragraphs
+                if (idx < song.notes.size - 1) {
+                    heightMm += metaLineHeight * 0.3f
+                }
             }
         }