docs: update README with direct profile switch and help flag

feat: add direct profile switch and help flag

docs: fix shell function in README and add -c flag usage

test: add tests for LoadProfiles with table-driven pattern

Initialize cursor at current active profile on startup

feat: add stability improvements and new CLI features

test: add tests for LoadCurrentContext and SaveCurrentContext

docs: update README to reflect current UI and features

feat: add error handling for missing or empty AWS profiles

feat: improve TUI UX with lipgloss styling and profile switch

chore: use English for all user-facing strings

docs: add README

feat: add spinner and async STS loading with bubbletea Cmd

feat: add profile switching with ~/.awsctx context file

feat: add bubbletea TUI with profile list and active profile indicator