feat: add {#{expression}} progress bar placeholder syntax - #567

Requested a reusable progress bar placeholder for leveling systems
(pets/jobs/items/collections/etc). StringUtils.createProgressBar
already existed but was never wired to anything usable from config.
Add a {#{expression}} bracket syntax, alongside the existing {{ }}/
{^{ }} math expression syntax, that evaluates the expression as a
0-100 percentage and renders it via createProgressBar with sensible
defaults (10 bars, green/gray). Works with any percentage-shaped
placeholder already exposed by any eco plugin, not just a specific
leveling system.

Adds a progress-bar section to config.yml (character, bars,
complete/in-progress/incomplete formats) and threads it through
PlaceholderParser instead of hardcoding the bar's look.