modeling: rebuild PEFT envoy paths on environment swap

[koriyoshi2041]

What changed

• remove the previous Hugging Face module tree from the shared Envoy registry before rebuilding after a PEFT wrap or unwrap
• preserve custom Envoy mappings across the rebuild
• assert that the server-side adapter path matches construction with peft= and that stale root paths are gone

PEFT retains the base model as a descendant of its wrapper. Without clearing the old registry entries, rebuilding reuses Envoys carrying pre-wrap paths and never constructs the base_model.model subtree.

Closes #726.

Tests

• fail-before: test_set_env_transitions reported model.transformer.h.0 instead of model.base_model.model.transformer.h.0
• CUDA_VISIBLE_DEVICES="" pytest tests/test_language.py::TestPeft -q — 5 passed
• git diff --check