delete messages + fix layout overflow

- DELETE /api/channels/{id}/messages/{msg_id} — soft delete, own only
- Broadcasts WsEvent::Delete to subscribers
- UI: "Del" button on hover for own messages (turns red)
- Fix layout: h-full + overflow-hidden on flex containers
- ScrollArea gets min-h-0 to properly constrain in flex
- Messages no longer push compose past viewport

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

ui/colony/src/App.tsx

@@ -1,7 +1,7 @@
 import { useCallback, useEffect, useRef, useState } from "react";
 import type { Channel } from "@/types/Channel";
 import type { Message } from "@/types/Message";
-import { getChannels, getMessages, getCurrentUsername } from "@/api";
+import { getChannels, getMessages, getCurrentUsername, deleteMessage } from "@/api";
 import { ChannelSidebar } from "@/components/ChannelSidebar";
 import { MessageItem } from "@/components/MessageItem";
 import { ComposeBox } from "@/components/ComposeBox";
@@ -121,12 +121,12 @@ export default function App() {
   );
 
   return (
-    <div className="flex h-full">
-      <div className="hidden md:block">
+    <div className="flex h-full overflow-hidden">
+      <div className="hidden md:flex md:flex-col md:h-full">
         {sidebar}
       </div>
 
-      <div className="flex-1 flex flex-col min-w-0">
+      <div className="flex-1 flex flex-col min-w-0 h-full overflow-hidden">
         <div className="px-4 py-3 md:px-6 md:py-4 border-b-2 border-border flex items-center gap-3">
           <Sheet open={sheetOpen} onOpenChange={setSheetOpen}>
             <SheetTrigger className="md:hidden p-1 h-8 w-8 text-muted-foreground hover:text-primary font-mono font-bold text-lg">
@@ -155,7 +155,7 @@ export default function App() {
           )}
         </div>
 
-        <ScrollArea ref={scrollRef} className="flex-1">
+        <ScrollArea ref={scrollRef} className="flex-1 min-h-0">
           {loading && messages.length === 0 ? (
             <div className="p-5 space-y-4">
               {[1, 2, 3].map((i) => (
@@ -178,12 +178,21 @@ export default function App() {
                 key={msg.id}
                 message={msg}
                 replyTarget={msg.reply_to ? messagesById.get(msg.reply_to) : undefined}
+                currentUsername={getCurrentUsername()}
                 onReply={(id) => {
                   const target = messagesById.get(id);
                   if (target) {
                     setReplyTo({ id, username: target.user.display_name, content: target.content });
                   }
                 }}
+                onDelete={async (chId, msgId) => {
+                  try {
+                    await deleteMessage(chId, msgId);
+                    loadMessages();
+                  } catch {
+                    // ignore
+                  }
+                }}
               />
             ))
           )}