refactor: remove branch selection functionality from install script

Simplifies install-pulse.sh by removing all branch installation capabilities to reduce script complexity and maintainability burden.

Removed:
- --branch command line argument
- prompt_for_branch_selection() function
- Branch validation and handling logic
- "Test a feature branch" menu options
- Branch-specific installation and update paths
- Branch status reporting

The script now only supports stable version tag installations, making it more focused and easier to maintain.

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

Author: rcourtman