fix: library row icons → outline SVG + context menu width

- library.html L591: item.icon (emoji) → self._renderIcon('file')
- library.html: +_renderIcon() helper with validNames filter
- app.css: context-menu min-width:200px → width:max-content + max-width:240px
- 143 tests passent

static/css/app.css

@@ -684,7 +684,8 @@ input, select, textarea { font-family: inherit; color: inherit; }
   border: 1px solid var(--border-light);
   border-radius: var(--radius-md);
   box-shadow: 0 8px 24px rgba(0,0,0,0.4);
-  min-width: 200px;
+  width: max-content;
+  max-width: 240px;
   padding: var(--space-xs) 0;
   z-index: 1000;
   display: none;