fix(slack): Slack channel fixes, DM filtering, emoji sanitization, and restore TLS on websocket

[sra]

…d TLS

Fixes several Slack adapter issues and restores the build after #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 fix(build): restore compile after security middleware + URL validation changes #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)

[jamiepine]

Looks good!