feat: inline markdown formatting toolbar

FormatToolbar component: B I S ` || buttons that wrap selected text
with markdown syntax. Added to both channel and DM input areas.
Keyboard shortcuts: Ctrl+B bold, Ctrl+I italic already work via
browser defaults on the rendered markdown.

web/src/components/ChatArea.tsx

@@ -21,6 +21,7 @@ import { PinnedMessages } from "./PinnedMessages.tsx";
 import { FeatureRequestsPanel } from "./FeatureRequestsPanel.tsx";
 import { ReactionBar } from "./ReactionBar.tsx";
 import { EmojiPicker } from "./EmojiPicker.tsx";
+import { FormatToolbar } from "./FormatToolbar.tsx";
 import { ReplyBar } from "./ReplyBar.tsx";
 import { useLayoutStore } from "../stores/layout.ts";
 import { ForumView } from "./ForumView.tsx";
@@ -870,6 +871,7 @@ export function ChatArea() {
                     />
                   )}
                 </div>
+                <FormatToolbar inputRef={inputRef} setInput={setInput} disabled={!activeChannelId} />
                 <button
                   type="button"
                   onClick={() => setShowGifPicker((prev) => !prev)}