Summary:
This PR resolves Linux dev environment issues by standardizing the Poetry virtualenv location and ensuring dev dependencies are reliably installed when building with dev=1. Adjust tiltfile, so that tilt performs clean reloads, when changes are triggered.

Changes:

• Standardize Poetry virtualenv to /opt/.venv across services.
• Set POETRY_VIRTUALENVS_CREATE=false and POETRY_VIRTUALENVS_IN_PROJECT=false to reuse the prebuilt venv.
• Export VIRTUAL_ENV and prepend /opt/.venv/bin to PATH in both build and runtime stages, including for nonroot.
• Add cache-busting tied to the dev build arg to force correct installation of dev dependencies.
• Clean up redundant PATH exports and ensure /etc/environment reflects the unified venv path.
• Adjust tiltfile sync and ignore during image build

Scope:

• services/admin-backend/Dockerfile
• services/document-extractor/Dockerfile
• services/mcp-server/Dockerfile
• services/rag-backend/Dockerfile

Fixes: #142