fix(web): gate native-only code out of the wasm build

The wasm check broke on the MCP `tools` op, the block library's folder
picker and DWG thumbnails, and the PDF export-window culling helpers.
Gate each one like the code around it; `read_handle` needs no gate.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

src/app/control/mod.rs

@@ -528,6 +528,7 @@ impl OpenCADStudio {
                 Task::none(),
             );
         }
+        #[cfg(not(target_arch = "wasm32"))]
         if op == "tools" {
             return (
                 json!({

src/app/update/blocks_palette.rs

@@ -77,6 +77,10 @@ impl OpenCADStudio {
             BlockPaletteMsg::ToggleOptions => {
                 self.block_palette.options_collapsed ^= true;
             }
+            // Browsers expose no folder picker.
+            #[cfg(target_arch = "wasm32")]
+            BlockPaletteMsg::LibraryBrowse => {}
+            #[cfg(not(target_arch = "wasm32"))]
             BlockPaletteMsg::LibraryBrowse => {
                 return Task::perform(
                     async {

src/io/pdf_export.rs

@@ -945,10 +945,12 @@ fn append_pdf_page(
     Ok(())
 }
 
+#[cfg(not(target_arch = "wasm32"))]
 /// Slack around the export window, in sheet mm, so a stroke whose centreline
 /// sits just outside still contributes its width.
 const CULL_MARGIN_MM: f64 = 10.0;
 
+#[cfg(not(target_arch = "wasm32"))]
 fn sheet_overlaps(b: [f64; 4], window: [f64; 4]) -> bool {
     b[0] <= window[2] + CULL_MARGIN_MM
         && b[2] >= window[0] - CULL_MARGIN_MM
@@ -956,6 +958,7 @@ fn sheet_overlaps(b: [f64; 4], window: [f64; 4]) -> bool {
         && b[3] >= window[1] - CULL_MARGIN_MM
 }
 
+#[cfg(not(target_arch = "wasm32"))]
 fn grow(bounds: &mut Option<[f64; 4]>, x: f64, y: f64) {
     if !x.is_finite() || !y.is_finite() {
         return;
@@ -967,6 +970,7 @@ fn grow(bounds: &mut Option<[f64; 4]>, x: f64, y: f64) {
     b[3] = b[3].max(y);
 }
 
+#[cfg(not(target_arch = "wasm32"))]
 /// Sheet-mm bounds of everything a wire inks (strokes, glyphs, fills).
 fn wire_sheet_bounds(wire: &WireModel, ox: f64, oy: f64, marker_h: f64) -> Option<[f64; 4]> {
     let mut bounds = None;
@@ -991,6 +995,7 @@ fn wire_sheet_bounds(wire: &WireModel, ox: f64, oy: f64, marker_h: f64) -> Optio
     bounds
 }
 
+#[cfg(not(target_arch = "wasm32"))]
 /// Sheet-mm bounds of a hatch, resolved the way `emit_hatch` places it.
 fn hatch_sheet_bounds(hatch: &HatchModel, ox: f64, oy: f64) -> Option<[f64; 4]> {
     let mut bounds = None;

src/io/thumbnail.rs

@@ -178,7 +178,6 @@ pub fn extract_to_png(input: &std::path::Path, output: &std::path::Path, size: u
 /// Read a DWG's embedded preview and decode it to an iced image handle for the
 /// Start page's recent-file thumbnails. `None` for DXF/other files, a missing
 /// preview, or an undecodable format (WMF).
-#[cfg(not(target_arch = "wasm32"))]
 pub fn read_handle(path: &std::path::Path) -> Option<iced::widget::image::Handle> {
     let img = dwg_thumbnailer::extract(path, MAX_DIM)?;
     let (w, h) = (img.width(), img.height());