feat: Add FPS limit setting from Blender editor - fixes #3018

[ipezygj]

Summary

Add Frame Rate Limit property to Blender editor so artists can set max FPS without logic nodes or hardcoding.

Problem

Currently:

• Armory runs at unlimited FPS by default
• No UI to set FPS limit
• Developers must use logic nodes or hardcode values
• Setting doesn't save with project

Solution

Blender UI (This PR)

1. Add 'Frame Rate Limit' property to Armory Scene panel
2. Uses Blender's built-in scene.render.fps
3. Saves automatically with .blend file
4. Shows helpful info about 0 = unlimited

Exporter (This PR)

Export FPS limit to scene config:

• Reads scene.render.fps during export
• Writes fps_limit to scene config if > 0
• Value persists in exported scene data

Runtime (Separate - recommended follow-up)

In Kha/Iron app initialization:

var fpsLimit = config.fps_limit ?? 0;
if (fpsLimit > 0) {
    // Apply frame rate limiting
    kha.Scheduler.setFramerate(fpsLimit);
}

Usage

1. Open Blender project in Armory
2. Go to Scene Properties → Armory Props
3. Set "Frame Rate Limit" to desired FPS (30, 60, 120, etc.)
4. Export project normally
5. Game will cap at specified FPS

Benefits

✅ Simple UI - no logic nodes
✅ Project-persistent - saves with .blend
✅ Uses standard Blender property
✅ Backward compatible (optional)
✅ Developer-friendly

Testing

• Set Frame Rate to 30/60/120
• Export and verify fps_limit in config
• Verify setting persists in .blend
• Confirm 0 (unlimited) works
• Check backward compat (missing setting = unlimited)

Files Changed

• armory/blender/arm/props_ui.py - Add UI property
• armory/blender/arm/exporter.py - Export FPS limit to config

Related

• Fixes Set FPS limit from the Blender editor #3018
• Follow-up PR needed: Runtime implementation in Kha/Iron startup

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Note: This PR handles Blender UI and export logic. Runtime frame rate limiting should be implemented in a follow-up PR (likely in App.hx or render loop initialization).