v3.15.2

Changes

• Refreshes product overview, evaluation onboarding, quickstart, tutorial, notebook-gallery, and API entry points for clearer buyer, evaluator, and developer understanding.
• Bumps package, citation, and lockfile metadata to 3.15.2 and refreshes capability inventory.
• Keeps release and container packaging version-independent where practical, including the Docker wheel install path.
• Aligns optional Qdrant backend testing with CI's locked install policy.

Verification

• GitHub CI green on 2a44c21: https://github.com/anulum/director-ai/actions/runs/26781046725
• Pre-commit, CodeQL, and OpenSSF Scorecard green on the same commit.
• Local push gates green: ruff-format, ruff-check, version-sync, bandit, and spdx-guard.