Implement LLM-WP-0007: Kimi K3 default and EUR spend reporting

Add moonshotai/kimi-k3 as OpenRouter basemodel default after live smoke,
USD→EUR cost conversion, append-only usage ledger, and CLI run/cost/spend
week commands with token and euro reporting.

tests/test_fx.py

@@ -0,0 +1,40 @@
+import pytest
+
+from llm_connect.fx import DEFAULT_EUR_PER_USD, FxRate, resolve_fx_rate
+
+
+def test_resolve_fx_prefers_explicit_rate():
+    rate = resolve_fx_rate(0.85)
+
+    assert rate is not None
+    assert rate.eur_per_usd == pytest.approx(0.85)
+    assert rate.source == "explicit"
+    assert rate.usd_to_eur(10.0) == pytest.approx(8.5)
+
+
+def test_resolve_fx_reads_env(monkeypatch):
+    monkeypatch.setenv("LLM_CONNECT_EUR_PER_USD", "0.9")
+
+    rate = resolve_fx_rate()
+
+    assert rate is not None
+    assert rate.eur_per_usd == pytest.approx(0.9)
+    assert rate.source == "env:LLM_CONNECT_EUR_PER_USD"
+
+
+def test_resolve_fx_falls_back_to_snapshot():
+    rate = resolve_fx_rate(env={})
+
+    assert rate is not None
+    assert rate.eur_per_usd == pytest.approx(DEFAULT_EUR_PER_USD)
+    assert rate.source.startswith("snapshot:")
+
+
+def test_invalid_env_rate_raises():
+    with pytest.raises(ValueError, match="LLM_CONNECT_EUR_PER_USD"):
+        resolve_fx_rate(env={"LLM_CONNECT_EUR_PER_USD": "0"})
+
+
+def test_fx_rate_rejects_non_positive():
+    with pytest.raises(ValueError, match="eur_per_usd"):
+        FxRate(eur_per_usd=-1, source="x")