FEAT GUI: Add seed-prompt inspiration entry points #2752

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

Browsing and single-example imports are shipped, but an empty composer still needs an obvious way to find seeds and return without losing context.

This is the next available, unassigned contributor item in #2744. #2751 completed through #3670. Claim this issue before starting; provider loading and selected-example scans remain later work.

Describe the solution you'd like

Add a compact "Need inspiration? Browse seed prompts" empty-chat callout and an accessible entry point near the composer. Reuse the existing Datasets route and navigation/draft handoff. Add a clear return-to-chat action when browsing originated in Chat; direct explorer entry must not imply an unrelated current destination.

Preserve text, whole conversation-editor drafts, per-turn media, target/scorer/objective/system/converter setup, attack/conversation identity, filters/cursors/selection and focus. Browsing remains target-free. Do not rebuild the state store or import engine.

Normal read-only memory/catalog/example GET requests are expected. Entry/return must not download providers, generate content, create attacks, send prompts or execute tools.

Complete this milestone's missing real-stack coverage now, not in #2761. Extend the seeded harness, which already covers text import into a new attack, with controlled conversation/media and saved-destination cases.

Acceptance criteria:

• Both entry points and contextual return work for empty unsaved Chat and saved conversations; direct explorer entry does not borrow unrelated context.
• Navigation/cancellation preserves drafts, setup, browse state and focus with keyboard and narrow-viewport coverage.
• Normal memory reads are allowed, but entry/return does not cause provider downloads, generation, attack creation, sends or tool execution.
• Real-backend Playwright fixtures cover a whole conversation and linked media, all three supported import destinations, and a nonempty-draft round trip without accidental sending. Respect existing sent-evidence and replacement rules.
• Component/routing tests cover entry/return and runtime changes; update the GUI guide. No privileged datasets or paid calls.

Describe alternatives you've considered, if relevant

No recommender/generation service, random downloads, onboarding redesign, second draft store or new import implementation. Keep fixes for any newly exposed import regression directly tied to these journeys, not an unrelated Chat refactor.

Additional context

Start with ChatInputArea, ChatWindow, App.handleNavigate, useChatDraftHandoff, existing Datasets routes, frontend/e2e/datasets.seeded.spec.ts and doc/gui/0_gui.md. Follow Fluent UI/accessibility/test conventions.

Technical prerequisite: #2751 and its completed foundations. Promoted under the November 4 reassessment; other open children remain gated. #2761 is a later integrated checkpoint, not a substitute for this coverage.