feat(chat): remove legacy bubble renderer, full-bleed is the only chat style (#881)

Deletes the ChatMessageList/ChatStreaming bubble path and the ChatStyle
setting (issue #866 phase 6). ChatScreen now renders FullBleedChatList
directly; ChatBubble becomes the user-message anchor with the shared
SystemBubble/InlineAttachment/formatTimestamp helpers intact. Stubs of
AuthManager.getChatStyle() removed from four test suites; TodoTaskCardTest
renders ToolBubble directly.

Verified: ktlintCheck green, testDebugUnitTest 962/962 pass, assembleDebug
APK builds.

Co-authored-by: M57 <hy4ri@users.noreply.github.com>

app/src/androidTest/java/com/m57/hermescontrol/ui/chat/TodoTaskCardTest.kt

@@ -42,7 +42,7 @@ class TodoTaskCardTest {
 
         composeTestRule.setContent {
             HermesControlTheme {
-                ChatBubble(message = message, isDarkTheme = true)
+                ToolBubble(message = message)
             }
         }
 
@@ -66,7 +66,7 @@ class TodoTaskCardTest {
 
         composeTestRule.setContent {
             HermesControlTheme {
-                ChatBubble(message = message, isDarkTheme = true)
+                ToolBubble(message = message)
             }
         }
 
@@ -90,7 +90,7 @@ class TodoTaskCardTest {
 
         composeTestRule.setContent {
             HermesControlTheme {
-                ChatBubble(message = message, isDarkTheme = true)
+                ToolBubble(message = message)
             }
         }
 
@@ -113,7 +113,7 @@ class TodoTaskCardTest {
 
         composeTestRule.setContent {
             HermesControlTheme {
-                ChatBubble(message = message, isDarkTheme = true)
+                ToolBubble(message = message)
             }
         }