Add VN variable interpolation in dialogue and HUD text #3
Description
Why
We already expose VN variables via [set/inc/dec/flag/unflag] and JES return props but authors cannot surface those values in dialogue or HUD without custom Java/interop. Dynamic text (e.g. showing player name, score, timers) is a common VN need and as currently authors must hardcode text or hack HUD calls per value
What to do
1.Add a lightweight placeholder format (e.g. ${var} or {var}) that resolves against VnState.getVariables()
2.Apply substitution when rendering/storing dialogue (before history entry) and when showing HUD messages, missing variables resolve to empty string
3. Keep compatibility so plain text unchanged, no recursion, simple string replacement is fine
4. Update docs/VNS Scripting/VNS Scripting.md with syntax and examples: Alice: Welcome back, ${playerName}!, [hud Score: ${score}]
Criteria
-Dialogue lines and [hud ...] may include placeholders; they render with current VN variable values
-Missing vars -> blank
-History stores the resolved text