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/benchmarks/quick_pptest.mjs

@@ -0,0 +1,31 @@
+// Quick PP+TG speed test
+const BASE = "http://127.0.0.1:8000";
+
+async function test(label, prompt, maxTok) {
+  const t0 = Date.now();
+  const r = await fetch(`${BASE}/v1/chat/completions`, {
+    method: "POST",
+    headers: { "Content-Type": "application/json" },
+    body: JSON.stringify({ model: "m", messages: [{ role: "user", content: prompt }], max_tokens: maxTok, temperature: 0 }),
+    signal: AbortSignal.timeout(600000),
+  });
+  const d = await r.json();
+  const dt = (Date.now() - t0) / 1000;
+  const u = d.usage || {};
+  const pp = u.prompt_tokens || 0;
+  const tg = u.completion_tokens || 0;
+  const ppSpeed = pp > 0 ? (pp / dt).toFixed(1) : "?";
+  const tgSpeed = tg > 0 ? (tg / dt).toFixed(1) : "?";
+  console.log(`${label} | PP:${pp}tok ${ppSpeed}t/s | TG:${tg}tok ${tgSpeed}t/s | ${dt.toFixed(1)}s`);
+}
+
+const short = "Count 1 to 20.";
+const long = "x".repeat(3000) + " Summarize above in 3 words.";
+const code = Array(200).fill("function foo(x) { return x * 2 + Math.random(); }").join("\n") + "\n\nRefactor above to arrow functions. Show first 5 lines.";
+
+await test("warmup", short, 20);
+await test("SHORT", short, 200);
+await test("3K-PP", long, 100);
+await test("10K-CODE", code, 100);
+await test("TG-500", short, 500);
+console.log("DONE");