feat(ui): configurable headline and subtitle via env vars

[opspawn]

Summary

Closes #1345

Adds two optional environment variables for customizing the kagent UI:

• NEXT_PUBLIC_HEADLINE: Replaces the default "Start a conversation" text shown in the chat interface before the first message is sent
• NEXT_PUBLIC_SUBTITLE: Optional tagline displayed below the "Agents" heading on the landing/agents pages

When neither variable is set, the UI behaves exactly as before — zero impact on default deployments.

Changes

File	Change
ChatInterface.tsx	Accept optional headline prop, fall back to "Start a conversation"
chat/page.tsx	Read NEXT_PUBLIC_HEADLINE and pass to ChatInterface
chat/[chatId]/page.tsx	Read NEXT_PUBLIC_HEADLINE and pass to ChatInterface
AgentList.tsx	Accept optional subtitle prop, render below "Agents" heading when set
page.tsx (root)	Read NEXT_PUBLIC_SUBTITLE and pass to AgentList
agents/page.tsx	Read NEXT_PUBLIC_SUBTITLE and pass to AgentList
layout.tsx	Add export const dynamic = "force-dynamic" for runtime env var reading

Testing

• All 107 existing unit tests pass
• TypeScript compilation clean (tsc --noEmit)
• ESLint clean on all modified files
• Without env vars set: UI renders identically to before
• With env vars set: custom headline/subtitle appear correctly

Usage

NEXT_PUBLIC_HEADLINE="Ask your agents anything" \
NEXT_PUBLIC_SUBTITLE="Powered by kagent" \
npm start

[Copilot]

Pull request overview

Adds support for customizing two UI strings via environment variables, enabling deployments to override the default chat greeting and optionally display a subtitle on Agents/landing pages.

Changes:

• Add optional headline prop to ChatInterface and render it in the empty-chat state.
• Add optional subtitle prop to AgentList and render it beneath the “Agents” heading when provided.
• Read NEXT_PUBLIC_HEADLINE / NEXT_PUBLIC_SUBTITLE from app routes and pass through to components; force dynamic rendering via root layout.

Reviewed changes

Copilot reviewed 7 out of 7 changed files in this pull request and generated 2 comments.

Show a summary per file

File	Description
ui/src/components/chat/ChatInterface.tsx	Accepts headline?: string and uses it instead of a hardcoded empty-chat heading.
ui/src/components/AgentList.tsx	Accepts subtitle?: string and conditionally renders it under the Agents heading.
ui/src/app/page.tsx	Reads NEXT_PUBLIC_SUBTITLE and passes it to AgentList on the root page.
ui/src/app/agents/page.tsx	Reads NEXT_PUBLIC_SUBTITLE and passes it to AgentList on the agents page.
ui/src/app/layout.tsx	Forces dynamic rendering (intended to enable runtime env-var reads).
ui/src/app/agents/[namespace]/[name]/chat/page.tsx	Reads NEXT_PUBLIC_HEADLINE and passes it to ChatInterface for new chats.
ui/src/app/agents/[namespace]/[name]/chat/[chatId]/page.tsx	Reads NEXT_PUBLIC_HEADLINE and passes it to ChatInterface for existing chats.

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[Copilot]

This page is a client component ("use client"), so process.env.NEXT_PUBLIC_HEADLINE will be inlined at build time in the browser bundle and won’t support runtime env-var overrides. To actually read the headline at runtime, move the env lookup into a server component (e.g., remove "use client" from this page, or add a server wrapper that reads the env var and passes it down as a prop).

[Copilot]

export const dynamic = "force-dynamic" on the root layout forces the entire app subtree to render dynamically, which can disable static optimization/caching site-wide and may not be “zero impact” operationally. Consider scoping dynamic rendering to only the routes that need runtime env reading (e.g., export dynamic = "force-dynamic" in the specific pages, or use a small server wrapper for just those pages/components).

Suggested change

	export const dynamic = "force-dynamic";
	export const dynamic = "auto";

[opspawn]

Closing in favor of #1347 by frank-bee which covers the same configurable headline/subtitle functionality.