docs: Update README for V0 release

[betegon]

Summary

Update the README to document all V0 commands and features.

Changes Needed

Add missing command documentation

• sentry org get command
• sentry project get command
• sentry event get command
• sentry issue explain command
• sentry issue fix command
• sentry auth refresh command

Add new features

• Magic @ selectors (@latest, @most_frequent)
• Short ID aliases for monorepo support
• DSN auto-detection from source code

Update examples

• Add monorepo usage examples
• Add AI commands examples
• Update issue commands with new options

Acceptance Criteria

• All V0 commands documented with examples
• Magic selectors explained
• Alias system explained
• DSN detection documented