test(mcp): comprehensive test suite — 95.8% coverage with race, integration, protocol tests

Add 6 test files covering all MCP server code paths:
- tools_internal_test.go: 27 direct tests for internal functions
- server_integration_test.go: 5 HTTP auth middleware tests
- concurrency_test.go: 3 race condition tests (270+ goroutines)
- protocol_test.go: 11 MCP protocol round-trip tests via in-process client
- tools_test.go: 12 edge-case SQL tests (CTEs, window functions, injections)
- server_test.go: 3 server lifecycle tests (start, shutdown, port-in-use)
- scripts/mcp-e2e-test.sh: JSON-RPC E2E shell script

Also fix go vet in Taskfile to exclude CGo-dependent pkg/cbinding.

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

Author: 2 people

Taskfile.yml

@@ -194,7 +194,7 @@ tasks:
     desc: Run go vet
     cmds:
       - echo "Running go vet..."
-      - go vet ./...
+      - go vet $(go list ./... | grep -v 'pkg/cbinding')
 
   lint:
     desc: Run golangci-lint