Improve thick-arrow syntax and rendering layout

[YeeShin504]

Summary

• Added variable thick-arrow syntax in parser: [start]=>[end] support and defaulting rules for partial thickness input.
• Added timeTickStep setting and updated tick rendering loop to draw ticks/grid at configured step intervals.
• Improved layout calculation for time-axis header overlap, annotation spacing, and right-side width buffering.
• Updated renderer thick-arrow drawing to support trapezoid-style variable start/end thickness and adjusted label placement.
• Updated docs editor reference/help content to include new syntax and settings examples.
• Refactored editor CSS to use root color variables and cleaned up layout styling consistency.
• Updated Pages deploy workflow to official upload/deploy-pages actions with separate build and deploy jobs.
• Updated docs build script so CI can set branch-specific output directory (dist for master, dist/dev for dev).