render: match Chrome font metrics with Liberation Sans/Serif/Mono

Chrome's default sans-serif on this class of host is Liberation Sans, not
DejaVu (measured: sans-serif == Arial == Helvetica == Liberation width,
DejaVu ~12% wider). Forcing DejaVu drifted all text wider and shifted
every line. Bundle Liberation Sans/Serif/Mono (DejaVu kept as glyph
fallback), default to Liberation Sans, and resolve font-family to the
right generic (monospace/code -> Mono, serif -> Serif, else -> Sans).
A controlled text page drops from ~15-20% to 3.5% pixel mismatch and
every line lands within 1px of Chrome.

crates/obscura-render/src/style.rs

@@ -333,6 +333,12 @@ fn apply_value(style: &mut LayoutStyle, name: &str, value: &str) {
             let bold = v == "bold" || v == "bolder" || v.parse::<u32>().map(|n| n >= 600).unwrap_or(false);
             style.font_weight = Some(if bold { "bold".to_string() } else { "normal".to_string() });
         }
+        "font-family" => {
+            let v = value.trim().to_ascii_lowercase();
+            if !v.is_empty() && v != "inherit" {
+                style.font_family = Some(v);
+            }
+        }
         // Our engine has no real inline formatting context, so text-align is
         // approximated the same way as align-items: it positions a block's
         // (or column-flex's) children along the cross axis. See