[codex] add context setup and env commands

[YoungJinJung]

Summary

• add unic context setup, unic context unset, and unic env CLI flows
• support one-step SSO account/role selection with config upsert/reuse
• copy setup/unset shell commands to the clipboard and document the new workflow

Why

Issue #69 asked for a one-step context setup flow that works well with local shell usage and does not mutate ~/.aws/credentials. This also adds a matching context unset flow to clear the selected context and reset shell env state quickly.

Details

• add config helpers for loading named contexts, upserting contexts, and unsetting the current context
• add env rendering for credential, assume-role, and concrete SSO contexts
• add interactive SSO setup that can log in, list accessible accounts/roles, and save a concrete context
• keep prompts on stderr and use clipboard copy for setup/unset shell commands
• extend README usage examples and behavior notes

Validation

• /opt/homebrew/bin/go test ./...
• /opt/homebrew/bin/go run ./cmd/unic context setup --help
• /opt/homebrew/bin/go run ./cmd/unic context unset --help

[amazon-q-developer]

Review Summary

I've completed a comprehensive review of PR #77 which adds unic context setup, unic context unset, and unic env CLI commands with SSO integration.

Changes Reviewed:

• New CLI commands for context management (internal/cli/context.go)
• SSO authentication and account/role listing (internal/services/aws/sso.go)
• Context setup workflow with interactive selection (internal/auth/setup.go, internal/auth/env.go)
• Config file manipulation helpers (internal/config/config.go)
• Comprehensive test coverage for all new functionality
• Updated README with usage examples

Assessment:
The implementation is well-structured with proper error handling, testability through function variable injection, and follows Go best practices. The code correctly implements the one-step SSO context setup flow described in issue #69 without mutating ~/.aws/credentials. All critical functionality has corresponding test coverage.

Approval Status: ✅ No blocking issues found. The code is ready for merge.

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