Add confirmation before Clear chat and Reset

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What is this about?

Problem

"Clear chat" and "Reset" wipe conversation state with one click — no confirmation.

Where to look

• index.html — clearHistory() (~1344), clearConversation() (~1354)

Acceptance criteria

• Confirmation shown when there is content/history to lose
• Cancel leaves state unchanged
• No confirmation when already empty

Skills needed

Small UX guardrail — confirm() or a simple inline modal.