Security:
- Remove instance/.secret_key and instance/stegasoo.db from git
- Add instance/ to .gitignore (was only ignoring frontends/web/instance/)
Lint fixes:
- Remove unused imports in temp_storage.py (os, shutil)
- Sort imports and fix f-string placeholders in cli.py
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Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>