CPLAT-9497: improve project-centric browser and line-art UI polish

[gavin-jeong]

JIRA: https://sendbird.atlassian.net/browse/CPLAT-9497

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Summary

• add project-centric session browser grouping, folding, and done-only filtering
• improve session and conversation rendering performance with preview/list caches and windowing
• surface monitor/background session state more clearly and polish TUI visuals with line-art icons and centered modals

Testing

• go test ./...
• go vet ./...

Security checklist (Infrastructure code)

• I have checked below conditions:
  • This PR doesn't contain any SecurityGroup rule changes which are not allowed via INF Jira ticket
  • This PR doesn't contain any public open SecurityGroup inbound rules(0.0.0.0/0) except the predefined service port
  • This PR doesn't contain any resources in a public subnet except those are needed with a specific technical reason
  • This PR doesn't contain any credentials (AWS Secret key, password, API tokens, etc)
  • This PR doesn't contain any IAM users which are not allowed via UAC Jira approval
  • The contents of this PR is following the guide from OSWAP and SendBird Secure Software Development Lifecycle