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.

llm_connect/fx.py

@@ -0,0 +1,93 @@
+"""USD to EUR conversion helpers for display and spend reporting.
+
+Rate tables remain USD-denominated (OpenRouter list prices). This module only
+converts already-estimated USD amounts into euros.
+"""
+
+from __future__ import annotations
+
+import os
+from dataclasses import dataclass
+from typing import Any
+
+
+# Snapshot: euros per one US dollar. Operator can override via env.
+DEFAULT_EUR_PER_USD = 0.92
+DEFAULT_FX_CAPTURED_AT = "2026-08-03"
+DEFAULT_FX_SOURCE = f"snapshot:{DEFAULT_FX_CAPTURED_AT}"
+ENV_EUR_PER_USD = "LLM_CONNECT_EUR_PER_USD"
+
+
+@dataclass(frozen=True)
+class FxRate:
+    """EUR conversion factor for one USD."""
+
+    eur_per_usd: float
+    source: str
+    captured_at: str = ""
+
+    def __post_init__(self) -> None:
+        rate = _positive_float("eur_per_usd", self.eur_per_usd)
+        source = str(self.source or "").strip()
+        if not source:
+            raise ValueError("source must be a non-empty string")
+        object.__setattr__(self, "eur_per_usd", rate)
+        object.__setattr__(self, "source", source)
+        object.__setattr__(self, "captured_at", str(self.captured_at or ""))
+
+    def usd_to_eur(self, amount_usd: float) -> float:
+        """Convert a USD amount to EUR."""
+        return float(amount_usd) * self.eur_per_usd
+
+
+def resolve_fx_rate(
+    explicit: FxRate | float | None = None,
+    *,
+    env: dict[str, str] | None = None,
+) -> FxRate | None:
+    """Resolve an FX rate from explicit value, environment, or bundled snapshot.
+
+    Resolution order:
+      1. *explicit* :class:`FxRate` or positive float (euros per USD)
+      2. Environment variable ``LLM_CONNECT_EUR_PER_USD``
+      3. Bundled snapshot rate
+
+    Returns ``None`` only when an explicit/env value is present but invalid
+    callers should pass nothing to get the snapshot. Empty env string falls
+    through to the snapshot.
+    """
+    if explicit is not None:
+        if isinstance(explicit, FxRate):
+            return explicit
+        return FxRate(
+            eur_per_usd=float(explicit),
+            source="explicit",
+            captured_at="",
+        )
+
+    environ = env if env is not None else os.environ
+    raw = environ.get(ENV_EUR_PER_USD)
+    if raw is not None and str(raw).strip() != "":
+        return FxRate(
+            eur_per_usd=_positive_float(ENV_EUR_PER_USD, raw),
+            source=f"env:{ENV_EUR_PER_USD}",
+            captured_at="",
+        )
+
+    return FxRate(
+        eur_per_usd=DEFAULT_EUR_PER_USD,
+        source=DEFAULT_FX_SOURCE,
+        captured_at=DEFAULT_FX_CAPTURED_AT,
+    )
+
+
+def _positive_float(name: str, value: Any) -> float:
+    if isinstance(value, bool):
+        raise ValueError(f"{name} must be a positive number")
+    try:
+        number = float(value)
+    except (TypeError, ValueError) as exc:
+        raise ValueError(f"{name} must be a positive number") from exc
+    if number <= 0:
+        raise ValueError(f"{name} must be a positive number")
+    return number