Add HEDL logo and fix WASM playground build

- Add SVG logo referenced in README (docs/assets/hedl-logo.svg)
- Fix pages.yml: exclude toon feature from WASM build because
  toon -> ratatui -> syntect -> onig_sys requires C compilation
  which is incompatible with wasm32-unknown-unknown target

Author: marcflp

.github/workflows/pages.yml

@@ -50,7 +50,7 @@ jobs:
           wasm-pack build crates/hedl-wasm \
             --target web \
             --out-dir playground/pkg \
-            --features all-formats
+            --features json,yaml,xml,csv
 
       - name: Prepare playground directory
         run: |