feat: Variet Engine v1.0 + 5-model tuning complete

Phase 01 (LLM Tuning):
- Gemma4 26B: 74.65 t/s (fast)
- Qwen 35B: 61.62 t/s (balanced)
- Gemma4 31B: 16.0 t/s (deep-coder)
- Qwen 27B: 16.7 t/s (deep-logic)
- Qwen 122B: 8.95 t/s (ultra, GPU 1 only)

Phase 02 (API Engine):
- FastAPI reverse proxy on port 8000
- /engine/switch hot-swap with 503 protection
- config/engine_models.json as single source of truth
- Replaced 4 individual .bat files with unified engine

File cleanup:
- scripts/ 85 files -> 9 + _archive/
- Root .bat files -> _archive/

scripts/_archive/q4km_latest.txt

@@ -0,0 +1,5 @@
+pure-GPU nommap small     |  62.29 | GPU | VRAM:22975 | ub=128 b=512 t=4
+pure-GPU ts=0.5,0.5       |  63.89 | GPU | VRAM:23002 | ub=128 b=512 t=4
+tune t=2                  |   64.1 | GPU | VRAM:22980 | ub=128 b=512 t=2
+tune t=6                  |  64.18 | GPU | VRAM:22982 | ub=128 b=512 t=6
+tune t=8                  |  63.11 | GPU | VRAM:22980 | ub=128 b=512 t=8