feat(slack): implement full Slack integration for CLI (#420)

Add cortex-slack crate with comprehensive Slack integration:

- Slack bot with Socket Mode (WebSocket) for real-time events
- Event handlers for @mentions and direct messages
- Slash commands (/cortex, /cortex-review)
- OAuth flow for workspace installation
- Message formatting (Markdown to Slack mrkdwn)
- Secure credential storage via OS keyring
- Comprehensive error handling for network/API errors
- 49 unit tests covering all modules

The integration supports:
- Bot OAuth tokens (xoxb-...)
- App-level tokens for Socket Mode (xapp-...)
- Signing secret for request verification
- Rate limiting handling with retry-after
- Token expiration and malformed API response handling

Modules:
- bot.rs: Main bot implementation with Socket Mode
- events.rs: Event parsing and handlers
- commands.rs: Slash command handling
- messages.rs: Block Kit message formatting
- oauth.rs: OAuth flow and routes
- config.rs: Configuration and keyring storage
- error.rs: Comprehensive error types

Co-authored-by: Droid Agent <droid@factory.ai>

Author: echobt

Cargo.toml

@@ -73,6 +73,9 @@ members = [
     "cortex-network-proxy",
     "cortex-shell-snapshot",
 
+    # CLI - Integrations
+    "cortex-slack",
+    
     # CLI - LM Studio Integration
     "cortex-lmstudio",
 
@@ -226,6 +229,9 @@ cortex-collab = { path = "cortex-collab" }
 cortex-network-proxy = { path = "cortex-network-proxy" }
 cortex-shell-snapshot = { path = "cortex-shell-snapshot" }
 
+# Integrations
+cortex-slack = { path = "cortex-slack" }
+
 # OpenTUI crates
 opentui = { path = "opentui-rs" }
 opentui-core = { path = "opentui-rs/crates/opentui-core" }

cortex-slack/Cargo.toml

@@ -0,0 +1,60 @@
+[package]
+name = "cortex-slack"
+version.workspace = true
+edition.workspace = true
+license.workspace = true
+description = "Slack integration for Cortex CLI - bot, events, and slash commands"
+
+[lints]
+workspace = true
+
+[dependencies]
+# Internal crates
+cortex-keyring-store = { path = "../cortex-keyring-store" }
+cortex-agents = { path = "../cortex-agents" }
+cortex-common = { path = "../cortex-common" }
+
+# Async runtime
+tokio = { workspace = true, features = ["full", "sync"] }
+tokio-stream = { workspace = true }
+async-trait = { workspace = true }
+futures = { workspace = true }
+
+# Web framework (for OAuth routes)
+axum = { workspace = true }
+tower = { workspace = true }
+tower-http = { workspace = true }
+
+# HTTP client
+reqwest = { workspace = true }
+hyper = { workspace = true }
+
+# Serialization
+serde = { workspace = true }
+serde_json = { workspace = true }
+
+# Error handling
+anyhow = { workspace = true }
+thiserror = { workspace = true }
+
+# Logging
+tracing = { workspace = true }
+
+# Utilities
+url = { workspace = true }
+chrono = { workspace = true }
+uuid = { workspace = true }
+base64 = { workspace = true }
+sha2 = { workspace = true }
+hmac = { workspace = true }
+hex = { workspace = true }
+secrecy = { workspace = true }
+urlencoding = { workspace = true }
+
+# WebSocket for Socket Mode
+tokio-tungstenite = { version = "0.24", features = ["native-tls"] }
+
+[dev-dependencies]
+tokio-test = { workspace = true }
+tempfile = { workspace = true }
+wiremock = { workspace = true }