feat: add pip install output filter

Parent: #717

## Problem

`pip install` outputs verbose download/build progress.

## Acceptance Criteria

- [ ] Match `pip install`, `pip3 install`, `python -m pip install`
- [ ] Strip download progress, build wheel output
- [ ] Preserve dependency conflicts, errors, and final summary
- [ ] Config: `[tools.filters.pip]` with `enabled` flag
- [ ] Tests
- [ ] Expected savings: 80-90%