refactor: require native samtools/minimap2, delete hand-rolled BAM/BAI code

fix: remove set -e from build.sh so curl failure doesn't abort build

fix: detect missing Vina binary at module level and download fallback; fail early if binary not found

fix: replace obabel CLI with NCI CACTUS API for SMILES→3D (eliminates all subprocess crashes)

fix: use obabel CLI subprocess for SMILES→3D (lightweight, no OOM) + Vina reads PDB receptor natively (no obabel PDBQT prep)

fix: eliminate obabel entirely — use RDKit for SMILES→3D + Vina PDB/SDF input (avoids OOM from obabel C++ subprocess)

fix: revert to BackgroundTasks + async DockingTool.run (no threads, no pybel); pre-download vina in build.sh

fix: simplify build.sh to only pip install (no risky binary downloads) + fix vina download path

fix: obabel self-healing — openbabel-wheel in requirements, runtime pip fallback, Vina download

fix: switch Render to Python buildpack with build.sh (openbabel via wheel, vina/phyml via wget)

fix: revert backend build to pip install (build.sh/apt-get broke the Render build, taking the backend down -> 404 on all routes incl. /api/audit)

fix: install openbabel/vina/phyml via build.sh in Python buildpack (deploy hook cannot switch runtime to docker)