refactor: remove X11 support and legacy window decoration code

[jardon]

Copied from #168 as a result of a mistake on my part.

Originally submitted by @CleoMenezesJr

📝 Description

This PR completely removes legacy support for X11, modernizing the codebase to focus exclusively on Wayland and recent GNOME versions (45+).

Key changes include:

• Removal of X11 Support: Deleted src/xprop.ts and all X11-specific methods in src/window.ts (e.g., xid, decorate, size_hint).
• Cleanup of Window Decorations: Removed the show_title setting and associated logic, as server-side decoration control via X11 properties is no longer applicable.
• Documentation Update: Updated README.md to remove X11-specific instructions and references.

This significantly reduces technical debt and simplifies the codebase.

Fixes #166

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🔍 Type of Change

• 🐛 Bug fix (non-breaking change that fixes an issue)
• ✨ New feature (non-breaking change that adds functionality)
• 💥 Breaking change (fix or feature that would cause existing functionality to change)
• 🧹 Code cleanup or refactor
• 🧪 Tests
• 📝 Documentation update
• ⚙️ CI/CD or build system update

Note: This is a breaking change for any users still attempting to use this extension on X11 sessions.

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✅ How Has This Been Tested?

• Build Verification: Ran make to ensure the project compiles successfully without the removed modules.
• Static Analysis: Performed grep searches to verify zero remaining references to xprop, X11.
• Manual Testing: Verified extension loading and core functionality on a Wayland session (GNOME 45+).

Test Configuration:

• OS: Linux (Fedora Silverblue / GNOME OS)
• Session: Wayland
• GNOME Version: 49

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📋 Checklist

Before submitting your PR, please check that:

• Code follows the project’s style guidelines
• I have self-reviewed my code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to documentation (if needed)
• My changes generate no new warnings
• I have added tests that prove my fix is effective or that my feature works
• New and existing unit tests pass locally with my changes