feat(html): scaffold op-html importer crate with public API

crates/op-html/Cargo.toml

@@ -0,0 +1,12 @@
+[package]
+name = "op-html"
+version.workspace = true
+edition = "2021"
+description = "HTML/CSS-subset importer: converts HTML into editable PenNode trees"
+license = "MIT"
+
+[dependencies]
+html5ever = "0.27"
+markup5ever_rcdom = "0.3"
+base64 = "0.22"
+jian-ops-schema = { path = "../../vendor/jian/crates/jian-ops-schema" }

crates/op-html/src/lib.rs

@@ -0,0 +1,63 @@
+//! HTML → PenNode importer (structured path, CSS-subset cascade).
+
+use jian_ops_schema::node::PenNode;
+
+pub struct HtmlImportOptions {
+    pub viewport_width: f64,
+    pub base_font_size: f64,
+    pub document_name: Option<String>,
+}
+
+impl Default for HtmlImportOptions {
+    fn default() -> Self {
+        Self {
+            viewport_width: 1440.0,
+            base_font_size: 16.0,
+            document_name: None,
+        }
+    }
+}
+
+pub struct HtmlImportResult {
+    pub nodes: Vec<PenNode>,
+    pub warnings: Vec<String>,
+}
+
+pub fn import_html(source: &str, opts: &HtmlImportOptions) -> HtmlImportResult {
+    let _ = opts;
+    let mut warnings = Vec::new();
+    if source.trim().is_empty() {
+        warnings.push("no importable content: input HTML is empty".to_string());
+        return HtmlImportResult {
+            nodes: Vec::new(),
+            warnings,
+        };
+    }
+    // Pipeline lands in later tasks; non-empty input is wired up in Task 11.
+    warnings.push("no importable content: importer pipeline not yet implemented".to_string());
+    HtmlImportResult {
+        nodes: Vec::new(),
+        warnings,
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn empty_input_yields_no_nodes_and_a_warning() {
+        let r = import_html("", &HtmlImportOptions::default());
+        assert!(r.nodes.is_empty());
+        assert_eq!(r.warnings.len(), 1);
+        assert!(r.warnings[0].contains("no importable content"));
+    }
+
+    #[test]
+    fn options_default_values() {
+        let o = HtmlImportOptions::default();
+        assert_eq!(o.viewport_width, 1440.0);
+        assert_eq!(o.base_font_size, 16.0);
+        assert!(o.document_name.is_none());
+    }
+}