fix: load system and platform fonts for diagram text rendering

Load fonts from system directories and Windows font path (WSL) into
fontdb. Map generic CSS families (sans-serif, serif, monospace) to
concrete fonts available in the database. This fixes text not appearing
in mermaid and graphviz diagram PNGs.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Author: JheisonMB

Cargo.lock

@@ -47,7 +47,6 @@ notify = { version = "7", features = ["macos_fsevent"] }
 # Mermaid diagram rendering
 mermaid-rs-renderer = { version = "0.2", default-features = false }
 resvg = "0.46"
-fontdb = "0.20"
 
 # Graphviz/DOT diagram rendering
 layout-rs = "0.1"

Cargo.toml

@@ -21,17 +21,10 @@ Self-contained LaTeX to PDF compiler — one curl, zero friction. No TeX Live, n
 
 ---
 
-### Demos
-
-#### Uso básico del CLI
+### Demo CLI
 
 ![Demo CLI](assets/texforge.gif)
 
-#### Integración con agentes en OpenCode
-
-![Demo OpenCode](assets/opencode.gif)
-
-
 ---
 
 ## Installation
@@ -105,6 +98,10 @@ An [texforge Skill](https://skills.sh/jheisonmb/skills/texforge) is available fo
 npx skills add https://github.com/jheisonmb/skills --skill texforge
 ```
 
+### Demo Agent with opencode
+
+![Demo OpenCode](assets/opencode.gif)
+
 ## Quick Start
 
 ```bash

README.md

@@ -212,15 +212,71 @@ fn resolve_tex(root: &Path, input: &str) -> PathBuf {
     }
 }
 
+/// Build a font database with system fonts and platform-specific fallbacks.
+fn build_fontdb() -> resvg::usvg::fontdb::Database {
+    use resvg::usvg::fontdb::Database;
+
+    let mut db = Database::new();
+    db.load_system_fonts();
+
+    // On WSL / Windows, also load the Windows font directory
+    let win_fonts = std::path::Path::new("/mnt/c/Windows/Fonts");
+    if win_fonts.is_dir() {
+        db.load_fonts_dir(win_fonts);
+    }
+
+    // If the DB still has no fonts at all, try common directories explicitly.
+    if db.is_empty() {
+        for dir in ["/usr/share/fonts", "/usr/local/share/fonts"] {
+            let p = std::path::Path::new(dir);
+            if p.is_dir() {
+                db.load_fonts_dir(p);
+            }
+        }
+    }
+
+    // Collect the set of available family names once (avoids borrow conflicts).
+    let available: std::collections::HashSet<String> = db
+        .faces()
+        .flat_map(|f| f.families.iter().map(|(name, _)| name.clone()))
+        .collect();
+
+    // Map generic CSS families to the first concrete font we find in the DB.
+    let sans = ["Arial", "DejaVu Sans", "Liberation Sans", "Noto Sans"];
+    if let Some(f) = sans.iter().find(|n| available.contains(**n)) {
+        db.set_sans_serif_family(*f);
+    }
+    let serif = [
+        "Times New Roman",
+        "DejaVu Serif",
+        "Liberation Serif",
+        "Noto Serif",
+    ];
+    if let Some(f) = serif.iter().find(|n| available.contains(**n)) {
+        db.set_serif_family(*f);
+    }
+    let mono = [
+        "Courier New",
+        "DejaVu Sans Mono",
+        "Liberation Mono",
+        "Noto Sans Mono",
+    ];
+    if let Some(f) = mono.iter().find(|n| available.contains(**n)) {
+        db.set_monospace_family(*f);
+    }
+
+    db
+}
+
 /// Convert SVG string to PNG bytes at 2x scale for print quality.
 fn svg_to_png(svg: &str) -> Result<Vec<u8>> {
-    let mut options = resvg::usvg::Options::default();
-    
-    // Load system fonts for text rendering
-    let mut fontdb = resvg::usvg::fontdb::Database::new();
-    fontdb.load_system_fonts();
-    options.fontdb = std::sync::Arc::new(fontdb);
-    
+    let fontdb = build_fontdb();
+
+    let options = resvg::usvg::Options {
+        fontdb: std::sync::Arc::new(fontdb),
+        ..Default::default()
+    };
+
     let tree = resvg::usvg::Tree::from_str(svg, &options).context("Failed to parse SVG")?;
 
     let scale = 2.0_f32;