feat: support inline images within song pages (Closes #2)

Add {image: path} directive to embed images at any position within a song's
sections. SongLine gains an optional imagePath field; when set, the line
represents an inline image rather than chord/lyric content. The renderer
scales and centers images within the content width. MeasurementEngine
reserves 40mm height per inline image for layout calculations.

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

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

@@ -43,15 +43,21 @@ class MeasurementEngine(
 
             // Lines in section
             for (line in section.lines) {
-                val hasChords = line.segments.any { it.chord != null }
-                val lyricHeight = fontMetrics.measureLineHeight(config.fonts.lyrics, config.fonts.lyrics.size)
-                if (hasChords) {
-                    val chordHeight = fontMetrics.measureLineHeight(config.fonts.chords, config.fonts.chords.size)
-                    heightMm += chordHeight + config.layout.chordLineSpacing + lyricHeight
+                if (line.imagePath != null) {
+                    // Inline image: estimate height as 40mm (default image block height)
+                    heightMm += 40f
+                    heightMm += 2f  // gap around image
                 } else {
-                    heightMm += lyricHeight
+                    val hasChords = line.segments.any { it.chord != null }
+                    val lyricHeight = fontMetrics.measureLineHeight(config.fonts.lyrics, config.fonts.lyrics.size)
+                    if (hasChords) {
+                        val chordHeight = fontMetrics.measureLineHeight(config.fonts.chords, config.fonts.chords.size)
+                        heightMm += chordHeight + config.layout.chordLineSpacing + lyricHeight
+                    } else {
+                        heightMm += lyricHeight
+                    }
+                    heightMm += 0.35f  // ~1pt gap between lines
                 }
-                heightMm += 0.35f  // ~1pt gap between lines
             }
 
             // Verse spacing

layout/src/test/kotlin/de/pfadfinder/songbook/layout/MeasurementEngineTest.kt

@@ -324,4 +324,40 @@ class MeasurementEngineTest {
         // Should be the same since no reference books are configured
         heightWith shouldBe heightWithout
     }
+
+    @Test
+    fun `inline image adds significant height`() {
+        val songWithImage = Song(
+            title = "With Image",
+            sections = listOf(
+                SongSection(
+                    type = SectionType.VERSE,
+                    lines = listOf(
+                        SongLine(listOf(LineSegment(text = "Line before"))),
+                        SongLine(imagePath = "images/test.png"),
+                        SongLine(listOf(LineSegment(text = "Line after")))
+                    )
+                )
+            )
+        )
+        val songWithoutImage = Song(
+            title = "No Image",
+            sections = listOf(
+                SongSection(
+                    type = SectionType.VERSE,
+                    lines = listOf(
+                        SongLine(listOf(LineSegment(text = "Line before"))),
+                        SongLine(listOf(LineSegment(text = "Line after")))
+                    )
+                )
+            )
+        )
+
+        val heightWith = engine.measure(songWithImage).totalHeightMm
+        val heightWithout = engine.measure(songWithoutImage).totalHeightMm
+
+        // Inline image adds ~42mm (40mm image + 2mm gap)
+        val diff = heightWith - heightWithout
+        diff shouldBeGreaterThan 30f  // should be substantial
+    }
 }