Slack was always marked as untested and is being dropped, leaving
Telegram as the sole supported platform.
- Delete the internal/platform/slack connector package
- Remove Slack registration in the platform factory
- Remove SlackConfig and its SLACK_TOKEN env vars from config
- Scrub Slack from README, docs, and .env examples
- Drop incidental Slack references from the gallerydl plugin copy
Also fixes a pre-existing staticcheck SA5011 warning in db_test.go
so the tree lints cleanly.
Felipe M.
29538b7d63