help: Update "Inbox" to document collapsed view.

- Replaces special link for logged-in users with instructions so that
  users can learn how to access this view.

Fixes #27326.

help/inbox.md

@@ -23,7 +23,7 @@ conversations.
 
 {tab|desktop-web}
 
-{relative|message|inbox}
+{!go-to-inbox.md!}
 
 1. Toggle **Include muted** next to the filter box at the top.
 
@@ -35,7 +35,7 @@ conversations.
 
 {tab|desktop-web}
 
-{relative|message|inbox}
+{!go-to-inbox.md!}
 
 1. Use the **Filter** box at the top to find a conversation.
    You can filter by stream, topic, or direct message participants.

help/include/go-to-inbox.md

@@ -0,0 +1,4 @@
+1. Click on <i class="zulip-icon zulip-icon-inbox"></i> **Inbox**
+   (or <i class="zulip-icon zulip-icon-inbox"></i> if the **views**
+   section is collapsed) in the left sidebar,
+   or use the <kbd>Shift</kbd> + <kbd>I</kbd> keyboard shortcut.

help/include/inbox-instructions.md

@@ -2,7 +2,7 @@
 
 {tab|desktop-web}
 
-{relative|message|inbox}
+{!go-to-inbox.md!}
 
 1. Click on a conversation you're interested in to view it. You can return to
    **Inbox** when done to select the next conversation.

help/marking-messages-as-read.md

@@ -73,7 +73,7 @@ stream or topic as read**.
 
 {tab|via-inbox-view}
 
-{relative|message|inbox}
+{!go-to-inbox.md!}
 
 1. Hover over a stream or topic in the left sidebar.