fix: preserve EP operational venv runtime identity

[pcvantol]

Problem

Resolving venv/bin/python followed its symlink to shared base Python. Distinct operational EP venvs could therefore collapse to one apparent runtime and the registration could point at a non-package base interpreter.

Change

• treats the absolute venv launcher spelling as operational-runtime identity while continuing to resolve durable data roots;
• applies the identity to record, resolver, package, inventory, and migration comparisons;
• distinguishes old service-referenced venvs that share a base interpreter;
• makes inventory coverage explicit: current-user explicit references are not proof of the Mac-wide one-installation invariant.

Validation

• full EP source suite: 1,416 tests passed;
• focused operational installation/update/migration suite: 20 tests passed;
• projection validation and diff check passed.

Depends on #154/#155. This does not perform a live cutover, service mutation, deletion, or Mac-wide verification.