prain: web UI with a model monitor

A clear chat page (markdown, code blocks with copy, stop, new chat, kept in the browser,
drafts shown as such) and a monitor sidebar, a sheet on phones: tokens/s, a live map of the
30 x 128 experts (in VRAM, used now, copied in), VRAM hit rate, copies, context, prompt cache,
GPU VRAM/load/temperature/power/fan. GET /status merges vLLM /metrics, amdgpu sysfs and the
stats file, which now lists the experts in VRAM. /warm answers 202 when a warm-up starts.
README: the int4 kernels, their A/B, 2048-token chunks as a trade, prompt logprobs limit.

tests/helpers.py

@@ -41,10 +41,13 @@ class StubVllm:
         self.delay = 0.0
         self.pause = 0.0
         self.fail = None
+        self.metrics = None  # Prometheus text served at GET /metrics
         stub = self
 
         class Handler(BaseHTTPRequestHandler):
             def do_GET(self):
+                if self.path == "/metrics" and stub.metrics is not None:
+                    return self.send(200, "text/plain", stub.metrics)
                 self.send(200, "application/json", {"data": [{"id": "stub-model"}]})
 
             def do_POST(self):