fix empty conversations message (#5108)

Fixes missing icons and adds a note about end-to-end encryption.

before / after

<img
src="https://github.com/user-attachments/assets/e5020c76-028a-4ccb-bd1c-8f2ffc219557"
width="320"/> <img
src="https://github.com/user-attachments/assets/88be21e0-b901-4ef1-b401-416eb262548f"
width="320"/>

Author: connyduck

app/src/main/java/com/keylesspalace/tusky/util/SpanUtils.kt

@@ -102,6 +102,8 @@ private val iconNameMapping: Map<String, Int> = mapOf(
     "{{search}}" to R.drawable.ic_search_24dp,
     "{{manage_accounts}}" to R.drawable.ic_manage_accounts_24dp,
     "{{chevron_right}}" to R.drawable.ic_chevron_right_24dp,
+    "{{public}}" to R.drawable.ic_public_24dp,
+    "{{edit}}" to R.drawable.ic_edit_24dp_filled
 )
 
 /**

app/src/main/res/values/strings.xml

@@ -830,7 +830,7 @@
     <string name="filter_description_format">%1$s: %2$s</string>
 
     <string name="help_empty_home">This is your <b>home timeline</b>. It shows the recent posts of the accounts you follow.\n\nTo explore accounts you can either discover them in one of the other timelines. For example the local timeline of your instance {{group}}. Or you can search them by name {{search}}; for example search for Tusky to find our Mastodon account.</string>
-    <string name="help_empty_conversations">Here are your <b>private messages</b>; sometimes called conversations or direct messages (DM).\n\nPrivate messages are created by setting the visibility {{public}} of a post to {{mail}} <i>Direct</i> and mentioning one or more users in the text.\n\nFor example you can start on the profile view of an account and tap the create button [iconics gmd_edit] and change the visibility.</string>
+    <string name="help_empty_conversations">Here are your <b>private messages</b>; sometimes called conversations or direct messages (DM).\n\nPrivate messages are created by setting the visibility {{public}} of a post to {{mail}} <i>Direct</i> and mentioning one or more users in the text.\n\nFor example you can start on the profile view of an account and tap the create button {{edit}} and change the visibility.\n\nNote that messages on the Fediverse are not end-to-end encrypted. Do not share any sensitive information.</string>
     <string name="help_empty_lists">This is your <b>lists view</b>. You can define a number of private lists and add accounts to that.\n\nNOTE that you can only add accounts you follow to your lists.\n\nThese lists can be used as a tab in Account preferences {{manage_accounts}} {{chevron_right}} Tabs.</string>
 
     <string name="load_newest_notifications">Load newest notifications</string>