…d TLS

Fixes several Slack adapter issues and restores the build after spacedriveapp#117.

Build fixes:
- Restore compile after security middleware changes (Axum State extractor
  pattern in api_auth_middleware, url::Url → reqwest::Url in browser tool)
(this is from unmerged pr spacedriveapp#125)

Slack DM filtering:
- DMs now bypass workspace/channel filters when sender is in dm_allowed_users
- dm_allowed_users is merged from both SlackConfig and per-binding configs
- Added debug logging for DM permission decisions

Emoji reactions:
- Sanitize Slack emoji reactions to use shortcodes via the `emojis` crate
- Handle edge case where emoji has no shortcode (falls back to name)
- Strip colons, normalize whitespace and casing

TLS connectivity:
- Add tokio-tungstenite with rustls-tls-native-roots feature to fix wss://
  connections that broke after the tungstenite 0.28 TLS feature restructure

Logging:
- Downgrade per-message Slack log from info to debug, matching Discord,
  Telegram, and Twitch adapters which only use info for lifecycle events

Style:
- Rename abbreviated `uid` to `sender_id` per style guide
- Remove section-divider comments and extra blank lines in imports

Tests:
- 9 unit tests for sanitize_reaction_name (unicode, shortcodes, fallbacks)
- 7 unit tests for SlackPermissions::from_config (merging, dedup, filtering)