feat: use Worte/Weise labels and render metadata at page bottom (Closes #5)

Add metadata_labels ("abbreviated"/"german") and metadata_position
("top"/"bottom") options to LayoutConfig. German labels use "Worte:" and
"Weise:" instead of "T:" and "M:", with "Worte und Weise:" when lyricist
and composer are the same person. Metadata at bottom position renders
after notes with word-wrapping. MeasurementEngine accounts for two-line
metadata in German label mode.

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

model/src/main/kotlin/de/pfadfinder/songbook/model/BookConfig.kt

@@ -51,7 +51,9 @@ data class LayoutConfig(
     val margins: Margins = Margins(),
     val chordLineSpacing: Float = 3f,    // mm
     val verseSpacing: Float = 4f,         // mm
-    val pageNumberPosition: String = "bottom-outer"
+    val pageNumberPosition: String = "bottom-outer",
+    val metadataLabels: String = "abbreviated",  // "abbreviated" (M:/T:) or "german" (Worte:/Weise:)
+    val metadataPosition: String = "top"  // "top" (after title) or "bottom" (bottom of last page)
 )
 
 data class Margins(