Merge branch 'main' into glitch-soc/merge-upstream

- `.env.production.sample`:
  Our sample config file is very different from upstream since it is much more
  complete. Upstream added documentation for a few env variables.
  Copied the new variables/documentation from upstream.
- `app/lib/feed_manager.rb`:
  Upstream added a timeline type (hashtags), while glitch-soc already had an
  extra one (direct messages). Not really a conflict but textually close
  changes.
  Ported upstream's changes.
- `app/models/custom_emoji.rb`:
  Upstream upped the custom emoji size limit, while glitch-soc had configurable
  limits.
  Upped the default limits accordingly.
- `streaming/index.js`:
  Upstream reworked how hastags were normalized. Minor conflict due to
  glitch-soc's handling of instance-local posts.
  Ported upstream's changes.

spec/lib/hashtag_normalizer_spec.rb

@@ -0,0 +1,29 @@
+# frozen_string_literal: true
+
+require 'rails_helper'
+
+describe HashtagNormalizer do
+  subject { described_class.new }
+
+  describe '#normalize' do
+    it 'converts full-width Latin characters into basic Latin characters' do
+      expect(subject.normalize('Ｓｙｎｔｈｗａｖｅ')).to eq 'synthwave'
+    end
+
+    it 'converts half-width Katakana into Kana characters' do
+      expect(subject.normalize('ｼｰｻｲﾄﾞﾗｲﾅｰ')).to eq 'シーサイドライナー'
+    end
+
+    it 'converts modified Latin characters into basic Latin characters' do
+      expect(subject.normalize('BLÅHAJ')).to eq 'blahaj'
+    end
+
+    it 'strips out invalid characters' do
+      expect(subject.normalize('#foo')).to eq 'foo'
+    end
+
+    it 'keeps valid characters' do
+      expect(subject.normalize('a·b')).to eq 'a·b'
+    end
+  end
+end