Fix search_list rendering "undefined" email fields when quick=true

Fixes #9. In quick mode, PonyMail's /api/stats.lua returns email objects
without subject/from/id, so the emails section rendered each entry as
"- **undefined**  From: undefined | ID: undefined". Quick mode is documented
as stats-only (emails_only exists for email summaries), so skip the emails
section entirely when quick=true. The subject/from/id fields are also guarded
with fallbacks so a sparse entry never renders as "undefined".

Verified live against dev@iceberg.apache.org (the reported repro): quick=true
now returns stats only; emails_only=true still renders populated subjects,
senders, and IDs.

Generated-by: Claude Code 2.1.158 (Claude Opus 4.8)