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.

contracts/functional/costs.md

@@ -1,7 +1,8 @@
 # Cost Estimates
 
 `llm_connect.costs` converts token estimates or observed token counts into
-USD estimates using `ModelRateRegistry`.
+USD estimates using `ModelRateRegistry`, and optionally into EUR via
+`llm_connect.fx`.
 
 ## Contract
 
@@ -9,6 +10,7 @@ USD estimates using `ModelRateRegistry`.
 from llm_connect import estimate_cost
 
 estimate = estimate_cost("openai/gpt-4o-mini", 28_000, 7_500)
+estimate = estimate_cost("moonshotai/kimi-k3", 1_000, 500, fx=0.92)
 ```
 
 For known models the result is:
@@ -17,9 +19,16 @@ For known models the result is:
 - `prompt_cost_usd`: prompt-token component.
 - `completion_cost_usd`: completion-token component.
 - `cost_source`: `rate_table:<model_id>`.
+- `cost_eur` / `prompt_cost_eur` / `completion_cost_eur`: EUR display amounts
+  when FX is available (default: bundled snapshot, override with `fx=` or
+  env `LLM_CONNECT_EUR_PER_USD` as euros-per-USD).
+- `fx_source`: how EUR was derived (`explicit`, `env:…`, `snapshot:…`).
 
-Unknown models return `CostEstimate(cost_usd=None, cost_source="unknown")`.
-Missing rates are never silently treated as zero cost.
+Unknown models return `CostEstimate(cost_usd=None, cost_source="unknown")`
+with EUR fields also `None`. Missing rates or FX are never silently treated
+as zero cost.
 
-The module also exposes `CostModel(registry=...)` for callers that prefer to
-carry a registry object and call `model.estimate_cost(...)`.
+Pass `apply_fx=False` to skip EUR conversion.
+
+The module also exposes `CostModel(registry=..., fx=...)` for callers that
+prefer to carry a registry object and call `model.estimate_cost(...)`.