fix: add scoped error logging for lexer/parser errors

- Add std.log.scoped(.pugz) to template.zig and view_engine.zig
- Log detailed error info (code, line, column, message) when parsing fails
- Log template path context in ViewEngine on parse errors
- Remove debug print from lexer, use proper scoped logging instead
- Move benchmarks, docs, examples, playground, tests out of src/ to project root
- Update build.zig and documentation paths accordingly
- Bump version to 0.3.1

examples/demo/views/pages/404.pug

@@ -0,0 +1,15 @@
+extends layouts/base.pug
+
+block title
+  title #{title} | Pugz Store
+
+block content
+  section.error-page
+    .container
+      .error-content
+        h1.error-code 404
+        h2 Page Not Found
+        p The page you are looking for does not exist or has been moved.
+        .error-actions
+          a.btn.btn-primary(href="/") Go Home
+          a.btn.btn-outline(href="/products") View Products