feat: support longer space names with dynamic icon widths and improved contrast

[Nicomalacho]

Summary

• Increase space name limit from 3 to 10 characters in the preferences UI text field
• Dynamically size menu bar icons based on text content instead of the fixed 49px width, so longer names display correctly
• Improve named spaces rendering: active space gets a filled rounded-rect background with cutout text; inactive spaces get a border with directly drawn text at 60% opacity for much better readability
• Update default fullscreen app name truncation from 3 to 10 characters

Motivation

The 3-character name limit is quite restrictive — users can't write readable labels like "Slack", "Browser", or "Terminal". This PR raises the limit to 10 characters and makes the rendering adapt to variable-length names.

The contrast improvement addresses poor readability of inactive space names, which were nearly invisible against certain menu bar backgrounds due to the destinationOut compositing on thin border icons.

Changes

File	Change
PreferencesView.swift	.prefix(3) → .prefix(10), updated placeholder text
SpaceObserver.swift	Fullscreen app default name .prefix(3) → .prefix(10)
IconCreator.swift	Dynamic icon width calculation, new createNamedIcons rendering with filled/bordered styles, variable-width mergeIcons layout

Screenshots

Tested on macOS Tahoe 26.2 with 16 spaces using full-word names (Slack, Monitor, Dev, Browser, etc.)