Bluesky _/~ => - characters in handles: docs, another test

for #982

templates/docs.html

@@ -308,6 +308,7 @@
 <li class="answer">
 <p>To bridge your fediverse account into Bluesky and interact with people there, search for and follow <code>@bsky.brid.gy@bsky.brid.gy</code>.</p>
 <p>If your fediverse account is <code>@[user]@[instance]</code>, your bridged account will have the handle <code>[user].[instance].ap.brid.gy</code> in Bluesky. For example, <a href="https://indieweb.social/@snarfed">@snarfed@indieweb.social</a> is bridged into Bluesky as <a href="https://bsky.app/profile/snarfed.indieweb.social.ap.brid.gy">@snarfed.indieweb.social.ap.brid.gy</a>.</p>
+<p>If your fediverse username has <code>_</code> (underscore) or <code>~</code> (tilde) characters, they're converted to <code>-</code> (dash) characters. For example, @a_b~c@my.social is bridged into Bluesky as @a-b-c.my.social.ap.brid.gy.
 <p>Bluesky limits profile bios to 256 characters, so if yours is longer in the fediverse, it will be truncated and ellipsized.</p>
 <p>Alternatively, <a href="#fediverse-follow">you can find and follow bridged Bluesky accounts</a> without bridging your own account, but they won't see your posts or interactions.<p>
 </li>

tests/test_atproto.py

@@ -660,8 +660,8 @@ class ATProtoTest(TestCase):
         mock_zone.return_value = zone = MagicMock()
         zone.resource_record_set = MagicMock()
 
-        Fake.fetchable = {'fake:user': ACTOR_AS}
-        user = Fake(id='fake:user')
+        Fake.fetchable = {'fake:us_er': ACTOR_AS}
+        user = Fake(id='fake:us_er')
         AtpRemoteBlob(id='https://alice.com/alice.jpg',
                       cid=BLOB_CID.encode('base32'), size=8).put()
 
@@ -674,7 +674,7 @@ class ATProtoTest(TestCase):
 
         # check DNS record
         zone.resource_record_set.assert_called_with(
-            name='_atproto.fake:handle:user.fa.brid.gy.', record_type='TXT',
+            name='_atproto.fake:handle:us-er.fa.brid.gy.', record_type='TXT',
             ttl=atproto.DNS_TTL, rrdatas=[f'"did={did}"'])
 
         # check profile record
@@ -697,7 +697,7 @@ class ATProtoTest(TestCase):
 
         uri = arroba.util.at_uri(did, 'app.bsky.actor.profile', 'self')
         self.assertEqual([Target(uri=uri, protocol='atproto')],
-                         Object.get_by_id(id='fake:user').copies)
+                         Object.get_by_id(id='fake:us_er').copies)
 
         mock_create_task.assert_called()