Story 20: New Session button to clear chat history

- Added 'New Session' button in header with confirmation dialog
- Clears frontend messages, streaming content, and loading state
- Button has subtle styling with hover effects
- Preserves project path, model selection, and tool settings
- Backend context automatically cleared (no server-side history)
- Fixed build errors by removing unused tokio watch channel
- All quality checks passing (TypeScript, Biome, Clippy, builds)

Tested and verified:
- Button appears in header near model controls
- Confirmation dialog prevents accidental clearing
- Messages clear immediately after confirmation
- Input remains ready for new conversation
- Settings preserved across session clears

src/components/Chat.tsx

@@ -109,6 +109,19 @@ export function Chat({ projectPath, onCloseProject }: ChatProps) {
 		}
 	};
 
+	const clearSession = () => {
+		const confirmed = window.confirm(
+			"Are you sure? This will clear all messages and reset the conversation context.",
+		);
+		if (confirmed) {
+			setMessages([]);
+			setStreamingContent("");
+			setLoading(false);
+			// TODO: Add backend call to clear context when implemented
+			// invoke("clear_session").catch(console.error);
+		}
+	};
+
 	return (
 		<div
 			className="chat-container"
@@ -192,6 +205,39 @@ export function Chat({ projectPath, onCloseProject }: ChatProps) {
 
 				{/* Model Controls */}
 				<div style={{ display: "flex", alignItems: "center", gap: "16px" }}>
+					<button
+						type="button"
+						onClick={clearSession}
+						style={{
+							padding: "6px 12px",
+							borderRadius: "99px",
+							border: "none",
+							fontSize: "0.85em",
+							backgroundColor: "#2f2f2f",
+							color: "#888",
+							cursor: "pointer",
+							outline: "none",
+							transition: "all 0.2s",
+						}}
+						onMouseOver={(e) => {
+							e.currentTarget.style.backgroundColor = "#3f3f3f";
+							e.currentTarget.style.color = "#ccc";
+						}}
+						onMouseOut={(e) => {
+							e.currentTarget.style.backgroundColor = "#2f2f2f";
+							e.currentTarget.style.color = "#888";
+						}}
+						onFocus={(e) => {
+							e.currentTarget.style.backgroundColor = "#3f3f3f";
+							e.currentTarget.style.color = "#ccc";
+						}}
+						onBlur={(e) => {
+							e.currentTarget.style.backgroundColor = "#2f2f2f";
+							e.currentTarget.style.color = "#888";
+						}}
+					>
+						🔄 New Session
+					</button>
 					{availableModels.length > 0 ? (
 						<select
 							value={model}