fix: persist privacy state to avoid repeated prompt and Settings Switch flash

[4pmtong]

Description

Related

• Builds on fix: patch help_improve bug #1455 and enhance: patch help_improve bug PR1455 #1456

Summary

Fix two privacy UX issues:

1. Repeated privacy prompt – "By messaging Eigent, you agree..." kept appearing on new project and when returning to chat
2. Settings Switch flash – Privacy Switch briefly showed wrong state (off↔on) when opening Settings

Changes

• localStorage persistence: Store privacy in eigent_privacy_enabled and eigent_privacy_enabled_${email} so ChatBox and Settings can show a cached state until the API loads
• Shared helpers in src/lib/privacy.ts: getStoredPrivacyEnabled(), setStoredPrivacyEnabled(), isPrivacyAllEnabled()
• Backend compatibility: Prefer res.all_required_granted when present, otherwise fall back to isPrivacyAllEnabled(res)
• ChatBox & Settings: Both use localStorage for init and update it on API responses and user actions

Testing Evidence

1. Enable privacy on home → create new project → prompt should not reappear
2. Open Settings → Privacy → Switch should not flash
3. Toggle privacy in Settings → return to ChatBox → state should stay in sync
4. Disable privacy → open Settings → Switch should show disabled without flashing

• I have included human-verified testing evidence in this PR.
• This PR includes frontend/UI changes, and I attached screenshot(s) or screen recording(s).
• No frontend/UI changes in this PR.

What is the purpose of this pull request?

• Bug fix
• New Feature
• Documentation update
• Other

Contribution Guidelines Acknowledgement

• I have read and agree to the Eigent Contribution Guideline

[a7m-1st]

Hi there @4pmtong thanks for the PR, we are actually removing the privacy consent from frontend in #1239 .
Looking forward to hear back!