refactor(markdown): extract MarkdownModels and MarkdownParser

Split AST block models and zero-Compose Markdown block parser into
ui/chat/markdown/ package. Wire into MarkdownText.

app/src/test/java/com/m57/hermescontrol/ui/chat/MarkdownTextBenchmark.kt

@@ -1,5 +1,6 @@
 package com.m57.hermescontrol.ui.chat
 
+import com.m57.hermescontrol.ui.chat.markdown.parseBlocks
 import org.junit.Test
 import kotlin.system.measureTimeMillis
 

app/src/test/java/com/m57/hermescontrol/ui/chat/MarkdownTextFeatureTest.kt

@@ -11,6 +11,10 @@ import com.m57.hermescontrol.theme.StatusRedContainer
 import com.m57.hermescontrol.theme.StatusYellow
 import com.m57.hermescontrol.theme.StatusYellowContainer
 import com.m57.hermescontrol.theme.searchHighlightColors
+import com.m57.hermescontrol.ui.chat.markdown.FnNote
+import com.m57.hermescontrol.ui.chat.markdown.MdBlock
+import com.m57.hermescontrol.ui.chat.markdown.TableAlign
+import com.m57.hermescontrol.ui.chat.markdown.parseBlocks
 import com.m57.hermescontrol.util.BidiUtils
 import org.junit.Assert.assertEquals
 import org.junit.Assert.assertFalse