fix: sidebar workspace tree + pages DB — emojis → outlined icons

Root cause: 3 sources d'icônes colorées dans le sidebar:
1. _workspace_tree_macro.html L28: {{ page.icon }} raw → filtré via valid_icons
2. db.py: DEFAULT '📄' → 'file'
3. board.py _file_icon(): 15 émojis → 'file'/'edit'/'image'
4. board.py/dashboard.py: JSON icon: 📄/📁 → file/folder
5. base.html L931: JS favorites icon → validNames filter
6. base.html render_tree_item: valid_icons list étendue + fallback

Migration: nouvelles pages utilisent 'file'/'folder'. Pages existantes
avec émojis → les templates utilisent le fallback automatiquement.
143 tests passent

app/templates/base.html

@@ -123,7 +123,7 @@
     {% else %}
       <span class="tree-toggle-placeholder"></span>
     {% endif %}
-    <span class="page-icon">{% if page.icon in ("folder","file","star","link","trash","book") %}{{ fd_icon(page.icon,14) }}{% else %}{{ page.icon }}{% endif %}</span>
+    <span class="page-icon">{% if page.icon in ("folder","file","star","link","trash","book","home","settings","lock","globe","image","edit","calendar","users","user","search","tag","bar-chart","grid","list","align-left","zap") %}{{ fd_icon(page.icon,14) }}{% elif page.icon and page.icon|length <= 2 %}{{ fd_icon("file",14) }}{% else %}{{ fd_icon("folder",14) }}{% endif %}</span>
     <span class="page-name">{{ page.name }}</span>
     <span class="item-actions">
       <button class="item-action-btn" @click.stop="newSubPage('{{ page.id }}')">+</button>
@@ -928,7 +928,11 @@
               favList.innerHTML = '<li class="sidebar-item empty-hint"><span class="page-icon page-icon-svg">'+getSvgIcon('star',16)+'</span><span class="page-name text-dim">No favorites yet</span></li>';
             } else {
               favList.innerHTML = items.map(function(item) {
-                var icon = item.icon || '<span class="page-icon-svg">'+getSvgIcon('file',14)+'</span>';
+                var iconName = item.icon || 'file';
+                // Map known icon names, anything else (including emojis) → file
+                var validNames = ['folder','file','star','link','trash','book','home','settings','lock','globe','image','edit','calendar','users','user','search','tag'];
+                if (validNames.indexOf(iconName) === -1) iconName = 'file';
+                var icon = '<span class="page-icon-svg">'+getSvgIcon(iconName,14)+'</span>';
                 const name = (item.title || 'Untitled');
                 const safeName = name.replace(/'/g, "\\'").replace(/"/g, '&quot;');
                 const url = item.url || ('/pages/' + item.id);