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/rates.md

@@ -8,7 +8,8 @@ post-hoc estimates.
 - `ModelRate` records `model_id`, prompt and completion rates in USD per
   1,000 tokens, `currency`, `source_url`, and `captured_at`.
 - `ModelRateRegistry.default()` returns the bundled OpenRouter snapshot
-  captured on `2026-05-17`.
+  (base rates captured `2026-05-17`; `moonshotai/kimi-k3` captured
+  `2026-08-03` at `$0.003` / `$0.015` per 1k prompt/completion).
 - `ModelRateRegistry.from_yaml(path)` accepts the package/consumer override
   shape:
 
@@ -21,10 +22,14 @@ rates:
   openai/gpt-4o-mini:
     prompt_per_1k: 0.00015
     completion_per_1k: 0.00060
+  moonshotai/kimi-k3:
+    prompt_per_1k: 0.003
+    completion_per_1k: 0.015
 ```
 
 - `merged_with(override)` returns a new registry where matching override
   entries replace default entries by `model_id`.
 
 Rates are a static snapshot. Consumers decide whether `captured_at` is fresh
-enough for their workflow.
+enough for their workflow. List prices remain USD; EUR display conversion is
+handled by `llm_connect.fx` / `estimate_cost`.