Expanded the help modal with:
- Absolute paths: starts with / or drive letter, used as-is
- Relative paths: ./backups, ../backups, ../../backups with table
showing URL-style conventions and resolved examples
- Placeholder paths: detailed descriptions of each placeholder
with current server values
- Recommended configurations table: single site, multi-site,
date-organized, per-profile, shared hosting
- Security warnings for web-root-accessible paths
- Help button uses JS click handler with Bootstrap 5 fallback
(fixes non-working tooltip icon)