Redesign README in KeyMood style

[Everyseok]

What changed

• rebuilt the README around the same information hierarchy and visual rhythm as KeyMood
• added a centered product hero, taskbar placement preview, badge row, comparison table, runtime model, display states, quick start, verification, requirements, troubleshooting, runtime contract, and author section
• added two repository-owned SVG preview assets with no external image dependency
• tightened the privacy description to match the implementation precisely

Why

The previous README documented the project but did not communicate the product visually or explain its runtime model with the same clarity as the KeyMood repository.

Impact

Visitors can now understand the widget, its placement, data source, privacy boundary, installation flow, and limitations from a single product-oriented README.

Verification

• rendered both SVG assets in Chromium and inspected them visually
• parsed both SVG files as XML
• verified every local README image/link target
• ran git diff --check
• ran build.ps1 successfully on Windows