ECHO-708 agentic chat add feature flag for frontend (#471)

<!-- This is an auto-generated comment: release notes by coderabbit.ai
-->
## Summary by CodeRabbit

* **New Features**
* Added a configurable toggle to enable or disable Agentic Chat
availability.
* The Agentic Chat option in the mode selector is hidden when disabled,
and the chat route falls back to the main chat UI.
* Administrators can control Agentic Chat visibility via deployment
configuration.
<!-- end of auto-generated comment: release notes by coderabbit.ai -->

Author: ussaama

echo/frontend/.env.example

@@ -7,6 +7,10 @@ VITE_ENABLE_CONVERSATION_HEALTH=0
 # Set to "1" to enable webhook configuration in project settings
 VITE_ENABLE_WEBHOOKS=0
 
+# Agentic Chat Feature
+# Set to "1" to enable the Agentic chat mode in the chat interface
+VITE_ENABLE_AGENTIC_CHAT=0
+
 # Other environment variables can be found in src/config.ts
 # Examples:
 # VITE_USE_PARTICIPANT_ROUTER=1

echo/frontend/src/components/chat/ChatModeSelector.tsx

@@ -16,6 +16,7 @@ import {
 	IconSparkles,
 } from "@tabler/icons-react";
 import { useState } from "react";
+import { ENABLE_AGENTIC_CHAT } from "@/config";
 import { analytics } from "@/lib/analytics";
 import { AnalyticsEvents as events } from "@/lib/analyticsEvents";
 import type { ChatMode } from "@/lib/api";
@@ -269,17 +270,19 @@ export const ChatModeSelector = ({
 
 				{/* Mode Cards */}
 				<Stack gap="lg">
-					<ModeCard
-						mode="agentic"
-						title={t`Agentic`}
-						subtitle={t`Delegate multi-step analysis with live tool execution`}
-						examples={getAgenticExamples()}
-						icon={IconSparkles}
-						isBeta
-						selectedMode={selectedMode}
-						isLoading={isLoading}
-						onSelectMode={handleSelectMode}
-					/>
+					{ENABLE_AGENTIC_CHAT && (
+						<ModeCard
+							mode="agentic"
+							title={t`Agentic`}
+							subtitle={t`Delegate multi-step analysis with live tool execution`}
+							examples={getAgenticExamples()}
+							icon={IconSparkles}
+							isBeta
+							selectedMode={selectedMode}
+							isLoading={isLoading}
+							onSelectMode={handleSelectMode}
+						/>
+					)}
 
 					<ModeCard
 						mode="deep_dive"

echo/frontend/src/config.ts

@@ -46,3 +46,5 @@ export const ENABLE_CONVERSATION_HEALTH = true;
 export const ENABLE_ANNOUNCEMENTS = true;
 export const ENABLE_DISPLAY_CONVERSATION_LINKS = true;
 export const ENABLE_WEBHOOKS = true;
+export const ENABLE_AGENTIC_CHAT =
+	import.meta.env.VITE_ENABLE_AGENTIC_CHAT === "1";

echo/frontend/src/routes/project/chat/ProjectChatRoute.tsx

@@ -24,11 +24,11 @@ import {
 import { useQueryClient } from "@tanstack/react-query";
 import { useEffect, useMemo, useRef, useState } from "react";
 import { useParams } from "react-router";
+import { AgenticChatPanel } from "@/components/chat/AgenticChatPanel";
 import {
 	ChatAccordionItemMenu,
 	ChatModeIndicator,
 } from "@/components/chat/ChatAccordion";
-import { AgenticChatPanel } from "@/components/chat/AgenticChatPanel";
 import { ChatContextProgress } from "@/components/chat/ChatContextProgress";
 import { ChatHistoryMessage } from "@/components/chat/ChatHistoryMessage";
 import { ChatMessage } from "@/components/chat/ChatMessage";
@@ -57,7 +57,11 @@ import { ScrollToBottomButton } from "@/components/common/ScrollToBottom";
 import { toast } from "@/components/common/Toaster";
 import { ConversationLinks } from "@/components/conversation/ConversationLinks";
 import { useConversationsCountByProjectId } from "@/components/conversation/hooks";
-import { API_BASE_URL, ENABLE_CHAT_AUTO_SELECT } from "@/config";
+import {
+	API_BASE_URL,
+	ENABLE_AGENTIC_CHAT,
+	ENABLE_CHAT_AUTO_SELECT,
+} from "@/config";
 import { useElementOnScreen } from "@/hooks/useElementOnScreen";
 import { useLanguage } from "@/hooks/useLanguage";
 import { useLoadNotification } from "@/hooks/useLoadNotification";
@@ -498,8 +502,10 @@ export const ProjectChatRoute = () => {
 		);
 	}
 
-	if (chatMode === "agentic") {
-		return <AgenticChatPanel chatId={chatId ?? ""} projectId={projectId ?? ""} />;
+	if (ENABLE_AGENTIC_CHAT && chatMode === "agentic") {
+		return (
+			<AgenticChatPanel chatId={chatId ?? ""} projectId={projectId ?? ""} />
+		);
 	}
 
 	return (
@@ -791,9 +797,7 @@ export const ProjectChatRoute = () => {
 										}}
 										rightSection={<IconSend size={24} />}
 										disabled={
-											normalizedInput.trim() === "" ||
-											isLoading ||
-											isSubmitting
+											normalizedInput.trim() === "" || isLoading || isSubmitting
 										}
 										{...testId("chat-send-button")}
 									>