fix(cmd): remove deprecated findings endpoints and broken vulnerabilities commands

[etienneddog]

Summary

Remove deprecated and broken security/vulnerability commands:

• security findings list and security findings get — API endpoints being deprecated by Datadog
• vulnerabilities search and vulnerabilities list — using wrong API methods (signals API instead of vulnerabilities API)

Changes

• Remove security findings list and security findings get commands, handlers, and flags from cmd/security.go
• Remove vulnerabilities top-level command entirely (both subcommands removed) from cmd/vulnerabilities.go and cmd/root.go
• Update tests in cmd/security_test.go and cmd/vulnerabilities_test.go
• security findings search and all static-analysis commands remain intact

Testing

• go build ./... passes
• go test ./cmd/... passes
• go vet ./cmd/... passes

Related Issues

N/A

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🤖 Generated with Claude Code

[github-actions]

📊 Test Coverage Report

Overall Coverage: 80.4%

Threshold: 80% ✅

Coverage by Package

## Coverage by Package

- github.com/DataDog/pup/pkg/auth/callback/server.go:40: 81.2%
- github.com/DataDog/pup/pkg/auth/dcr/client.go:28: 100.0%
- github.com/DataDog/pup/pkg/auth/dcr/types.go:24: 100.0%
- github.com/DataDog/pup/pkg/auth/oauth/client.go:22: 100.0%
- github.com/DataDog/pup/pkg/auth/oauth/pkce.go:24: 85.7%
- github.com/DataDog/pup/pkg/auth/storage/factory.go:53: 94.7%
- github.com/DataDog/pup/pkg/auth/storage/keychain.go:44: 42.9%
- github.com/DataDog/pup/pkg/auth/storage/storage.go:58: 71.4%
- github.com/DataDog/pup/pkg/auth/types/types.go:23: 100.0%
- github.com/DataDog/pup/pkg/client/client.go:32: 94.4%
- github.com/DataDog/pup/pkg/config/config.go:22: 100.0%
- github.com/DataDog/pup/pkg/formatter/formatter.go:31: 100.0%
- github.com/DataDog/pup/pkg/useragent/useragent.go:32: 100.0%
- github.com/DataDog/pup/pkg/util/time.go:20: 95.8%

## Summary

total:								(statements)		80.4%

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📈 Coverage Status: ✅ PASSED - Coverage meets minimum threshold

_{Updated for commit d0004e6}