fix(mcp): resolve TOCTOU race condition and resource leak

- Use atomic.Bool for closed flag to prevent TOCTOU race between
  CallTool and Close operations
- Add double-check pattern in CallTool for thread-safe closed state
- Use atomic Swap in Close to ensure no new calls can start after
  closed flag is set
- Move MCP manager cleanup defer before initialization to handle
  partial initialization failures
- Update tests to use atomic.Bool operations

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

go.mod

@@ -8,6 +8,7 @@ require (
 	github.com/bwmarrin/discordgo v0.29.0
 	github.com/caarlos0/env/v11 v11.3.1
 	github.com/chzyer/readline v1.5.1
+	github.com/gdamore/tcell/v2 v2.13.8
 	github.com/google/uuid v1.6.0
 	github.com/gorilla/websocket v1.5.3
 	github.com/larksuite/oapi-sdk-go/v3 v3.5.3
@@ -16,6 +17,7 @@ require (
 	github.com/mymmrac/telego v1.6.0
 	github.com/open-dingtalk/dingtalk-stream-sdk-go v0.9.1
 	github.com/openai/openai-go/v3 v3.22.0
+	github.com/rivo/tview v0.42.0
 	github.com/slack-go/slack v0.17.3
 	github.com/spf13/cobra v1.10.2
 	github.com/stretchr/testify v1.11.1
@@ -35,7 +37,6 @@ require (
 	github.com/dustin/go-humanize v1.0.1 // indirect
 	github.com/elliotchance/orderedmap/v3 v3.1.0 // indirect
 	github.com/gdamore/encoding v1.0.1 // indirect
-	github.com/gdamore/tcell/v2 v2.13.8 // indirect
 	github.com/inconshreveable/mousetrap v1.1.0 // indirect
 	github.com/lucasb-eyer/go-colorful v1.3.0 // indirect
 	github.com/mattn/go-colorable v0.1.14 // indirect
@@ -44,7 +45,6 @@ require (
 	github.com/petermattis/goid v0.0.0-20260113132338-7c7de50cc741 // indirect
 	github.com/pmezard/go-difflib v1.0.0 // indirect
 	github.com/remyoudompheng/bigfft v0.0.0-20230129092748-24d4a6f8daec // indirect
-	github.com/rivo/tview v0.42.0 // indirect
 	github.com/rivo/uniseg v0.4.7 // indirect
 	github.com/rs/zerolog v1.34.0 // indirect
 	github.com/spf13/pflag v1.0.10 // indirect