chore: silence native and wasm build warnings

Gate target-specific code so neither build warns about the other's items:
native-only helpers (view, window icon, file dialogs, file association, plugin
host/guard/registry, self-update) are cfg'd to non-wasm; the wasm-only font
fallback (script_of / cjk_lang / request) is cfg'd to wasm. Drop an unused mut,
allow the few genuinely-conditional dead items (mesh_click_hit, GPU layout
helpers, parity stubs), and gate the embedded PlotSettings-unrelated dead
constants. Both targets now build clean (only the unavoidable nom/quick-xml
future-incompat dependency notice remains).

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

src/scene/text/ttf_glyph.rs

@@ -205,6 +205,7 @@ fn shape_cache() -> &'static Mutex<ShapeCache> {
 
 /// Pixel font size the layout runs at. Positions and outlines are normalized
 /// out of pixel space afterwards, so the exact value only affects rounding.
+#[allow(dead_code)]
 const SHAPE_FS: f32 = 1000.0;
 
 /// Shared cosmic-text layout engine, loaded once with the system fonts. Held

src/scene/text/web_font.rs

@@ -57,6 +57,7 @@ impl Script {
 /// 2 = Korean. Set from the active document's code page.
 static CJK_LANG: AtomicU8 = AtomicU8::new(0);
 
+#[cfg(target_arch = "wasm32")]
 fn cjk_lang() -> Script {
     match CJK_LANG.load(Ordering::Relaxed) {
         1 => Script::Japanese,
@@ -83,6 +84,7 @@ pub fn set_cjk_lang_from_codepage(code_page: &str) -> bool {
 
 /// The script font that covers `ch`, or `None` for control / uncovered code
 /// points. Ranges mirror the subset unicode ranges in `web/fonts/generate.sh`.
+#[cfg(target_arch = "wasm32")]
 pub fn script_of(ch: char) -> Option<Script> {
     Some(match ch as u32 {
         0x0000..=0x024F | 0x1E00..=0x1EFF | 0x2000..=0x206F => Script::Latin,
@@ -184,6 +186,8 @@ mod imp {
     use super::Script;
     use std::sync::Arc;
 
+    // Kept for parity with the wasm impl; only the wasm path has a caller.
+    #[allow(dead_code)]
     pub fn request(_script: Script) -> Option<Arc<Vec<u8>>> {
         None
     }
@@ -196,4 +200,7 @@ mod imp {
     }
 }
 
-pub use imp::{fetch, insert, request, take_pending};
+pub use imp::{fetch, insert, take_pending};
+// `request` only has a caller in the wasm font-fallback path.
+#[cfg(target_arch = "wasm32")]
+pub use imp::request;