Issue 005: Local dashboard and history

[cody257]

Summary

• Adds browser-local conversation persistence using localStorage.
• Adds a landing-page local dashboard for recent conversations.
• Supports conversation statuses: active, accepted, declined, expired.
• Lets users reopen saved local conversations and clear local history.
• Adds e2e coverage for saving and reopening a chat session.

Verification

• npm run lint
• npm test
• npm run test:e2e
• npm run build
• npm audit --audit-level=moderate

Notes

• No auth, database, cloud sync, billing, or API model added.
• Data is stored only in the current browser.