Update CLI install proposal and plan: multi-host + module detection

Multi-host support:
- Stage 3 changed from single-select menu to checkbox (all hosts pre-selected)
- Non-interactive mode accepts multiple --agent flags
- Deploy artifacts to all selected hosts in a single run
- Added multi-host test cases

Module detection simplification:
- Detect at Maven/Gradle build file level (pom.xml, build.gradle*)
- Root has build file? Show only "." (entire project as one unit)
- Root has no build file? Show immediate children with build files
- Prevents overwhelming users with nested Maven modules in large projects
- Updated test cases to reflect simplified detection logic

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

Author: HumanBean17