v6.1.6 services stack: wave-2/3 audit hardening

Services-only stack hardening from waves 2-3 of the parallel audit loop.

Commits: 4e46516 (API), 658e396 (LLM sandbox), 76ae57e (voice), aad12e8 (ops), e57646b (art-data), 5e9e0b3 (installer), plus daemon/deadcode/security follow-ups.

Closed: wave-1 #2261-#2275, wave-2 actionable #2277-#2357/#2359-#2404 (fixed+verified, 1217 passed / 1 skipped / 1 pre-existing scipy failure; test_fp8_scaled_mm.py excluded order-dependent CUDA segfault #2276).

Still open: #2274 dep majors (blocked upstream), #2276 flake, #2358/#2363/#2364/#2365 owner-decision, #2399 docs follow-up, #2405-#2410 omnibus trackers.