v0.8.0 — 3D printing checks (M12)

4 new tools: check_printability (thin walls, overhangs/bridges, small & horizontal holes, bed adhesion, score + fix candidates), estimate_print (material, mass, filament length, time, cost), suggest_orientation (6 orientations + current, optional apply), apply_print_fixes (elephant-foot chamfer, hole compensation, teardrop holes). Material table PLA/PETG/ABS/ASA/TPU/NYLON with nozzle/layer profile. 31 tools, 232 headless tests.