Fix nip30303 tag parsing bugs

WordStatisticsTag.parse used has(3) but the tag has only 3 elements
(indices 0-2), so the guard never passed and parse always returned null
— silently breaking all Chapter and Chunk event parsing. Correct to
has(2).

Also replace unsafe tag[n].toInt() with toIntOrNull() in WordStatisticsTag
and IndexTag so a malformed numeric field from a relay returns null
instead of throwing NumberFormatException up through the parse loop.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

composeApp/src/commonMain/kotlin/press/mantra/compose/nostr/nip30303/tags/IndexTag.kt

@@ -16,9 +16,10 @@ class IndexTag(
         fun parse(tag: Array<String>): IndexTag? {
             ensure(tag.has(1)) { return null }
             ensure(tag[0] == TAG_NAME) { return null }
-            // TODO: Check that it is an int...
+
+            val index = tag[1].toIntOrNull() ?: return null
             return IndexTag(
-                index = tag[1].toInt(),
+                index = index,
             )
         }
 

composeApp/src/commonMain/kotlin/press/mantra/compose/nostr/nip30303/tags/WordStatisticsTag.kt

@@ -16,12 +16,15 @@ class WordStatisticsTag(
         const val TAG_NAME = "word_stats"
 
         fun parse(tag: Array<String>): WordStatisticsTag? {
-            ensure(tag.has(3)) { return null }
+            ensure(tag.has(2)) { return null }
             ensure(tag[0] == TAG_NAME) { return null }
 
+            val wordCount = tag[1].toIntOrNull() ?: return null
+            val characterCount = tag[2].toIntOrNull() ?: return null
+
             return WordStatisticsTag(
-                wordCount = tag[1].toInt(),
-                characterCount = tag[2].toInt(),
+                wordCount = wordCount,
+                characterCount = characterCount,
             )
         }