fix(preview): match Kitty's cell metrics and rendering more closely

- line-height: 1.45 -> 1.25 to match Kitty's default cell_height ratio so
  rows pack to terminal density instead of web-text density.
- font-kerning: none (terminals never kern monospace fonts).
- text-rendering: geometricPrecision plus WebKit/Mozilla font smoothing,
  so cells stay on integer pixel grids and characters don't shift on
  hinting boundaries.
- Wider fallback stack: Liberation Mono before generic monospace, so
  Linux preview without web fonts looks right.
- Selection drops the 2px border-radius. Real Kitty fills selected cells
  as full rectangles, no rounding.

Author: Confitty Developer

src/components/live-preview/terminal-screen.component.ts

@@ -46,7 +46,8 @@ function isAnsiKey(value: string): value is AnsiKey {
       min-height: 1em;
     }
     .selected {
-      border-radius: 2px;
+      /* Match Kitty cell selection: square fill, no rounding. */
+      padding: 0 0.05em;
     }
     .url {
       text-underline-offset: 2px;

src/components/live-preview/terminal-window.component.ts

@@ -141,10 +141,14 @@ export class TerminalWindowComponent {
     return {
       backgroundColor: rgba(colors.background, opacity),
       color: colors.foreground,
-      fontFamily: `"${fonts.font_family}", ui-monospace, SFMono-Regular, Menlo, Consolas, monospace`,
+      fontFamily: `"${fonts.font_family}", ui-monospace, SFMono-Regular, Menlo, Consolas, "Liberation Mono", monospace`,
       fontSize: `${px}px`,
-      lineHeight: '1.45',
+      lineHeight: '1.25',
       fontVariantLigatures: ligatures,
+      fontKerning: 'none',
+      textRendering: 'geometricPrecision',
+      WebkitFontSmoothing: 'antialiased',
+      MozOsxFontSmoothing: 'grayscale',
       borderRadius: '10px',
       outline: borderWidth ? `${borderWidth}px solid ${w.active_border_color}` : 'none',
       outlineOffset: borderWidth ? `-${borderWidth}px` : '0',