refactor: narrow zeph-tools re-export surface

**Epic**: #1977

zeph-tools lib.rs re-exports 40+ types including internal implementation details.
Audit and reduce to necessary public API.

**Acceptance Criteria**:
- [ ] Internal types not re-exported at crate root
- [ ] All downstream crates still compile
- [ ] Public API documented

**Complexity**: Medium | **Effort**: 2h
**Ref**: ABS-03