fix(core): shared page mode syncing (#14756)

### Summary
This fixes a few inconsistencies in shared page behavior:
fixes https://github.com/toeverything/AFFiNE/issues/14751
- shared pages now open in the correct published mode when the URL does
not already include ?mode=...
- switching between page and edgeless in shared mode now keeps the URL
query param in sync
- the default Copy Link action now follows the current editor mode
- shared viewers can toggle between page and edgeless mode in readonly
share pages

---

### What Changed
- updated shared page mode resolution to prefer URL mode, with backend
publish mode as fallback
- added query-param syncing for shared page mode changes
- made the default share link copy use:
  - page link in page mode
  - edgeless link in edgeless mode
- allowed EditorModeSwitch to toggle both ways in shared mode
- extracted shared-mode behavior into small hooks to keep share-page.tsx
cleaner

---

### Demo

https://www.loom.com/share/a287172321fb4fc5b94f7c67a39298a9


<!-- This is an auto-generated comment: release notes by coderabbit.ai
-->
## Summary by CodeRabbit

* **New Features**
* Mode switching between page and edgeless no longer blocked by shared
gating; shared pages initialize and respect the resolved editor mode.
* Shared page URLs stay in sync with editor mode and copy-link actions
include/preserve the selected mode.

* **Tests**
* Added tests for publish-mode resolution, query-string mode handling,
and default share-mode behavior.

* **Bug Fixes**
  * Updated shared-page “not found” UI text to match new messaging.
<!-- end of auto-generated comment: release notes by coderabbit.ai -->

---------

Co-authored-by: DarkSky <25152247+darkskygit@users.noreply.github.com>

packages/frontend/core/src/components/hooks/affine/use-register-copy-link-commands.tsx

@@ -3,9 +3,12 @@ import {
   registerAffineCommand,
 } from '@affine/core/commands';
 import { useSharingUrl } from '@affine/core/components/hooks/affine/use-share-url';
+import { getDefaultShareMode } from '@affine/core/components/hooks/affine/use-share-url.utils';
+import { EditorService } from '@affine/core/modules/editor';
 import { useIsActiveView } from '@affine/core/modules/workbench';
 import type { WorkspaceMetadata } from '@affine/core/modules/workspace';
 import { track } from '@affine/track';
+import { useLiveData, useService } from '@toeverything/infra';
 import { useEffect } from 'react';
 
 export function useRegisterCopyLinkCommands({
@@ -18,6 +21,7 @@ export function useRegisterCopyLinkCommands({
   const isActiveView = useIsActiveView();
   const workspaceId = workspaceMeta.id;
   const isCloud = workspaceMeta.flavour !== 'local';
+  const currentMode = useLiveData(useService(EditorService).editor.mode$);
 
   const { onClickCopyLink } = useSharingUrl({
     workspaceId,
@@ -42,12 +46,14 @@ export function useRegisterCopyLinkCommands({
         icon: null,
         run() {
           track.$.cmdk.general.copyShareLink();
-          isActiveView && isCloud && onClickCopyLink();
+          isActiveView &&
+            isCloud &&
+            onClickCopyLink(getDefaultShareMode(currentMode));
         },
       })
     );
     return () => {
       unsubs.forEach(unsub => unsub());
     };
-  }, [docId, isActiveView, isCloud, onClickCopyLink]);
+  }, [currentMode, docId, isActiveView, isCloud, onClickCopyLink]);
 }

packages/frontend/core/src/components/hooks/affine/use-share-url.utils.ts

@@ -0,0 +1,7 @@
+import type { DocMode } from '@blocksuite/affine/model';
+
+export const getDefaultShareMode = (
+  currentMode?: DocMode
+): DocMode | undefined => {
+  return currentMode === 'edgeless' ? 'edgeless' : undefined;
+};