Phase 1.4: Unit tests for foundation and core commands

[omattsson]

Overview

Comprehensive unit tests for CLI foundation packages and core stack commands.

Tasks

• HTTP client tests with mock server (auth headers, error handling, status codes)
• Config loading tests (file, env vars, flags, precedence, multi-context)
• Output formatter tests (table, JSON, YAML for each resource type)
• Command flag parsing tests for all stack subcommands
• Token storage and expiry tests
• 80%+ coverage on pkg/client, pkg/config, pkg/output

Acceptance Criteria

• go test ./... -v passes
• Coverage report shows 80%+ on pkg/ packages

Depends On

• Phase 1.3: Core stack instance lifecycle commands #3