FEAT GUI: Add seed-prompt inspiration entry points

Start with frontend\src\components\Chat\ChatInputArea.tsx, ChatWindow.tsx, App.tsx, and the dataset routes/context added in earlier work items. Read the existing context-preservation and explorer entry points before following the frontend style and test instructions. Done means both chat entry points, return behavior, direct explorer entry, accessibility, narrow viewports, and routing/component tests meet the listed acceptance criteria without triggering fetches or attack creation.

Is your feature request related to a problem? Please describe.

A dataset explorer is hard to discover when a user is staring at an empty chat composer and needs a seed prompt. The journey must feel like an extension of chat rather than abandoning the current attack.

Work item 8 of 17 in #2744. Technical prerequisites: dataset browsing and the completed draft/import flow in items 3-7. Keep not ready yet until promoted.

Describe the solution you'd like

Add a compact "Need inspiration? Browse seed prompts" callout in the empty-chat state and an accessible entry point near the composer. Both navigate to the existing Datasets section through the shared context-preservation mechanism.

Provide a clear return-to-chat action in the explorer when reached from chat. Preserve the source attack/conversation, the user's draft, and the explorer's filters/selection. From a standalone dataset route, do not pretend an unrelated attack is the current destination.

Browsing is available without a target. The later import action explains any target/destination requirements. Keep the callout lightweight and consistent with the current layout, themes, and touch-target conventions.

Acceptance criteria:

• Both entry points reach the explorer and returning restores the original draft/context.
• A user can start from an empty unsaved chat or an existing conversation.
• Keyboard navigation, accessible labels, focus restoration, and narrow viewports work.
• No dataset fetch, attack creation, or target call happens just by using the callout.
• Routing/component tests cover navigation, return, and direct explorer entry.

Describe alternatives you've considered, if relevant

No AI prompt-generation service, recommender, full onboarding redesign, or automatic random dataset download is needed. The useful first step is an obvious route to existing seeds.

Additional context

Start with frontend\src\components\Chat\ChatInputArea.tsx, ChatWindow.tsx, App.tsx, and the dataset routes/context added earlier. Follow the frontend style/test instructions. This completes the first milestone: browsing memory and using one example in chat.