Fix cli.py running in wrong working directory.

Previously, cli.py ran in <repo-root>/files. However, our relative
paths assume the working directory is <repo-root>. This resulted in
sanitize.render_emoji L153 to improperly return false when checking
for the presence of 'files/assets/images/emojis/{emoji}.webp',
leading to emojis in notifications sent by cli.py-invoked tasks to
not be rendered to HTML.

files/cli.py

@@ -2,6 +2,13 @@ from .__main__ import app, db_session, cache
 from flask import g
 import files.helpers.cron
 
+import os
+from pathlib import Path
+
+# cli.py runs in <repo-root>/files, whereas our relative paths assume
+# the WD is <repo-root>. NOTE: Change this if cli.py is ever moved.
+os.chdir(Path(__file__).parent.parent)
+
 #from flask_migrate import Migrate
 #from flask_sqlalchemy import SQLAlchemy
 #import files.classes