Add homelab dashboards: system, LLM, and UPS on one domain

Three dashboards served by one FastAPI app with a SQLite history store
(raw / 1m / 1h) and hand-written SVG charts: no Prometheus, no Grafana,
no CDN, no build step. Nothing is fetched from the internet at runtime.

* system: a stdlib-only agent (agent/host_agent.py) reports /proc and
  /sys counters; the dashboard turns them into rates over a labelled
  window, so every number says how it was measured.
* llm: gufo/llama.cpp and vLLM /metrics are parsed by an in-house
  exposition parser. Measured delta/elapsed throughput beats a native
  per-request gauge, and each value carries its provenance.
* ups: a NUT wire-protocol client plus health checks that name what
  they looked at. Commands are gated by NUT_ALLOW_ACTIONS,
  DASH_READ_ONLY and a DANGER confirmation, re-checked server-side.

Missing values render as n/a rather than 0, and an unconfigured source
answers 404 {"configured": false} without dialling anything, so "not
deployed here" never looks like an outage.

253 tests at 94% coverage against captured real fixtures; ruff and
pyright clean.

LLM-Generated: true

tests/conftest.py

@@ -0,0 +1,71 @@
+"""Shared fixtures: real captures for shape, fakes for behaviour.
+
+Anything that must match an upstream (an agent snapshot, an engine's /metrics text, the NUT
+wire protocol) is asserted against a verbatim capture in tests/fixtures/. Everything that
+needs a *failure* — a dead host, a refused command, a counter reset — is a fake here.
+"""
+from __future__ import annotations
+
+import json
+import sys
+from pathlib import Path
+from typing import Any
+
+import pytest
+
+ROOT = Path(__file__).resolve().parents[1]
+SRC = ROOT / "src"
+if str(SRC) not in sys.path:
+    sys.path.insert(0, str(SRC))
+
+from dashboards.rates import RateEstimator  # noqa: E402
+from dashboards.store import SampleStore  # noqa: E402
+
+FIXTURES = Path(__file__).resolve().parent / "fixtures"
+
+
+@pytest.fixture
+def db(tmp_path: Path) -> Any:
+    store = SampleStore(tmp_path / "t.sqlite3")
+    try:
+        yield store
+    finally:
+        store.close()
+
+
+@pytest.fixture
+def store(db: Any) -> Any:
+    """Alias: some tests read better with `store`, others with `db`. Same object."""
+    return db
+
+
+@pytest.fixture
+def agent_snapshot() -> dict[str, Any]:
+    """A real driveripper snapshot (Threadripper + R9700, 48 logical CPUs)."""
+    return json.loads((FIXTURES / "agent_driveripper.json").read_text())
+
+
+@pytest.fixture
+def agent_snapshots() -> dict[str, dict[str, Any]]:
+    """Every captured host, keyed by name — fleet code paths need >1 host to mean anything."""
+    out: dict[str, dict[str, Any]] = {}
+    for path in sorted(FIXTURES.glob("agent_*.json")):
+        out[path.stem.removeprefix("agent_")] = json.loads(path.read_text())
+    return out
+
+
+@pytest.fixture
+def metrics_text() -> Any:
+    """metrics_text('gufo') / metrics_text('vllm') -> the captured exposition verbatim."""
+    def load(engine: str) -> str:
+        path = FIXTURES / f"metrics_{engine}.txt"
+        if not path.exists():
+            pytest.skip(f"missing fixture {path.name} — run scripts/capture-fixtures.sh --with-llm")
+        return path.read_text()
+
+    return load
+
+
+@pytest.fixture
+def rates() -> RateEstimator:
+    return RateEstimator(span=10.0)