fix(cmd): prevent panic in test command with empty API keys

[platinummonkey]

Summary

Fixed a panic in the pup test command that occurred when API keys were not set (e.g., when using OAuth2 authentication).

Problem

The test command attempted to slice API keys for masking without checking if they existed or had sufficient length, causing a panic:

panic: runtime error: slice bounds out of range [:8] with length 0

This occurred because config validation only requires Site to be set, allowing empty API keys when OAuth2 authentication is used.

Changes

• Added length checks before slicing API/App keys in test command (root.go:210-227)
• Display appropriate messages based on key length:
  • Empty: Shows "(not set - using OAuth2 or will prompt)"
  • Too short (<12 chars): Shows key with warning "(too short - may be invalid)"
  • Valid (≥12 chars): Shows masked version "xxxxxxxx...yyyy"
• Added comprehensive tests covering all edge cases (root_test.go:235-320):
  • TestTestCmd_EmptyKeys - Empty API keys don't panic
  • TestTestCmd_ShortKeys - Short keys display warning
  • TestTestCmd_ValidKeys - Valid keys are properly masked
  • TestTestCmd_InvalidSite - Validation still enforces required Site

Testing

# Empty keys (OAuth2 scenario)
./pup test
# Output: "API Key: (not set - using OAuth2 or will prompt)"

# Valid keys
DD_API_KEY="..." DD_APP_KEY="..." ./pup test
# Output: "API Key: 12345678...7890"

# Short keys
DD_API_KEY="short" DD_APP_KEY="key" ./pup test
# Output: "API Key: short (too short - may be invalid)"

# All tests pass
go test ./cmd/... -v -run TestTestCmd

🤖 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 54c9eee}