feat: Add update_theme functionality with UI support

Backend:
- Add PUT /api/themes/:id endpoint for updating existing themes

Store:
- Add updateTheme method to theme store

MCP:
- Add update_theme tool to modify name, description, or save current variables

UI:
- Add edit button to ThemeListItem (custom themes only)
- Add edit modal with name and description fields
- Support editing from both desktop sidebar and mobile dropdown

frontend/src/services/tools/themeTools.ts

@@ -6,6 +6,7 @@ export const THEME_TOOLS = [
   'get_active_theme',
   'set_theme_variable',
   'save_theme',
+  'update_theme',
   'list_themes',
   'switch_theme',
   'set_default_theme',
@@ -212,6 +213,85 @@ export function registerThemeTools() {
     }
   )
 
+  // update_theme
+  registerTool(
+    'update_theme',
+    'Actualiza un tema existente (nombre, descripción o variables)',
+    {
+      type: 'object',
+      properties: {
+        theme: {
+          type: 'string',
+          description: 'Nombre o ID del tema a actualizar'
+        },
+        name: {
+          type: 'string',
+          description: 'Nuevo nombre para el tema (opcional)'
+        },
+        description: {
+          type: 'string',
+          description: 'Nueva descripción para el tema (opcional)'
+        },
+        saveCurrentVariables: {
+          type: 'boolean',
+          description: 'Si es true, guarda las variables actuales (con los cambios de set_theme_variable) en este tema'
+        }
+      },
+      required: ['theme']
+    },
+    async (args: { theme: string; name?: string; description?: string; saveCurrentVariables?: boolean }) => {
+      try {
+        const themeStore = useThemeStore()
+        await themeStore.fetchThemes()
+
+        // Find theme by ID or name
+        const theme = themeStore.themes.find(t =>
+          t.id === args.theme || t.name.toLowerCase() === args.theme.toLowerCase()
+        )
+
+        if (!theme) {
+          const available = themeStore.themes.map(t => t.name).join(', ')
+          return `Tema "${args.theme}" no encontrado.\nDisponibles: ${available}`
+        }
+
+        if (theme.is_system) {
+          return `No se puede modificar "${theme.name}" porque es un tema del sistema. Usa save_theme para crear una copia.`
+        }
+
+        // Build update data
+        const updateData: { name?: string; description?: string; variables?: any } = {}
+
+        if (args.name) {
+          updateData.name = args.name
+        }
+        if (args.description !== undefined) {
+          updateData.description = args.description
+        }
+        if (args.saveCurrentVariables) {
+          const variablesToSave = themeStore.previewTheme || themeStore.activeTheme?.variables
+          if (variablesToSave) {
+            updateData.variables = variablesToSave
+          }
+        }
+
+        if (Object.keys(updateData).length === 0) {
+          return 'No se especificaron cambios. Usa name, description o saveCurrentVariables.'
+        }
+
+        await themeStore.updateTheme(theme.id, updateData)
+
+        const changes = []
+        if (args.name) changes.push(`nombre: "${args.name}"`)
+        if (args.description !== undefined) changes.push('descripción actualizada')
+        if (args.saveCurrentVariables) changes.push('variables guardadas')
+
+        return `Tema "${theme.name}" actualizado:\n  ${changes.join('\n  ')}`
+      } catch (e: any) {
+        return `Error al actualizar tema: ${e.message}`
+      }
+    }
+  )
+
   // list_themes
   registerTool(
     'list_themes',