feat: open template via URL in linear mode (#6945)

## Summary

Adds `mode` as a valid url query param when opening template from URL.



https://github.com/user-attachments/assets/8e7efb1c-d842-4953-822a-f3cea7ddecb6

┆Issue is synchronized with this [Notion
page](https://www.notion.so/PR-6945-feat-open-template-via-URL-in-linear-mode-2b76d73d365081d8ad4af3d49a68a4ff)
by [Unito](https://www.unito.io)

src/platform/workflow/templates/composables/useTemplateUrlLoader.ts

@@ -4,6 +4,7 @@ import { useRoute, useRouter } from 'vue-router'
 
 import { clearPreservedQuery } from '@/platform/navigation/preservedQueryManager'
 import { PRESERVED_QUERY_NAMESPACES } from '@/platform/navigation/preservedQueryNamespaces'
+import { useCanvasStore } from '@/renderer/core/canvas/canvasStore'
 
 import { useTemplateWorkflows } from './useTemplateWorkflows'
 
@@ -13,9 +14,10 @@ import { useTemplateWorkflows } from './useTemplateWorkflows'
  * Supports URLs like:
  * - /?template=flux_simple (loads with default source)
  * - /?template=flux_simple&source=custom (loads from custom source)
+ * - /?template=flux_simple&mode=linear (loads template in linear mode)
  *
  * Input validation:
- * - Template and source parameters must match: ^[a-zA-Z0-9_-]+$
+ * - Template, source, and mode parameters must match: ^[a-zA-Z0-9_-]+$
  * - Invalid formats are rejected with console warnings
  */
 export function useTemplateUrlLoader() {
@@ -24,7 +26,10 @@ export function useTemplateUrlLoader() {
   const { t } = useI18n()
   const toast = useToast()
   const templateWorkflows = useTemplateWorkflows()
+  const canvasStore = useCanvasStore()
   const TEMPLATE_NAMESPACE = PRESERVED_QUERY_NAMESPACES.TEMPLATE
+  const SUPPORTED_MODES = ['linear'] as const
+  type SupportedMode = (typeof SUPPORTED_MODES)[number]
 
   /**
    * Validates parameter format to prevent path traversal and injection attacks
@@ -34,12 +39,20 @@ export function useTemplateUrlLoader() {
   }
 
   /**
-   * Removes template and source parameters from URL
+   * Type guard to check if a value is a supported mode
+   */
+  const isSupportedMode = (mode: string): mode is SupportedMode => {
+    return SUPPORTED_MODES.includes(mode as SupportedMode)
+  }
+
+  /**
+   * Removes template, source, and mode parameters from URL
    */
   const cleanupUrlParams = () => {
     const newQuery = { ...route.query }
     delete newQuery.template
     delete newQuery.source
+    delete newQuery.mode
     void router.replace({ query: newQuery })
   }
 
@@ -70,6 +83,24 @@ export function useTemplateUrlLoader() {
       return
     }
 
+    const modeParam = route.query.mode as string | undefined
+
+    if (
+      modeParam &&
+      (typeof modeParam !== 'string' || !isValidParameter(modeParam))
+    ) {
+      console.warn(
+        `[useTemplateUrlLoader] Invalid mode parameter format: ${modeParam}`
+      )
+      return
+    }
+
+    if (modeParam && !isSupportedMode(modeParam)) {
+      console.warn(
+        `[useTemplateUrlLoader] Unsupported mode parameter: ${modeParam}. Supported modes: ${SUPPORTED_MODES.join(', ')}`
+      )
+    }
+
     try {
       await templateWorkflows.loadTemplates()
 
@@ -87,6 +118,9 @@ export function useTemplateUrlLoader() {
           }),
           life: 3000
         })
+      } else if (modeParam === 'linear') {
+        // Set linear mode after successful template load
+        canvasStore.linearMode = true
       }
     } catch (error) {
       console.error(