fix(billing): 过期规则 URL 不再让整个 profile 失效（降级应用 + 点名 URL）

生产现网发现（issue #1 排查）：billing.rules 里一条指向
https://opencode.ai/inference/v1 的规则，在该源 base_url 变成
.../inference/openai/v1 之后匹配不到任何源；严格编译因此让**整个** profile
不生效 —— 账单恒 0、unpriced_reqs 涨到 3.7 万，唯一痕迹是一行启动日志。

- 严格编译失败时降级为 lenient：应用能匹配的规则，其余按 profile default；
- 日志用 ERROR 点名**具体哪条 URL** 写错（新增 billing.UnmatchedRuleURLs），
  并说明未匹配流量的记账去向；
- 判据 TestBillingStaleRuleURLStillAppliesOtherRules：一条过期规则 + 一条有效
  规则 ⇒ 有效规则必须仍然生效。

internal/billing/compile.go

@@ -106,6 +106,27 @@ func CompileOpts(profile *config.BillingProfile, sources []config.Source, lenien
 	return prices, nil
 }
 
+// UnmatchedRuleURLs lists the non-wildcard rule URLs that match no configured
+// source. Compile() treats such a URL as a hard error (a typo'd rule prices
+// nothing), but the CALLER needs the list to say which rule to fix instead of
+// just "compile failed" — and to explain what the degraded table dropped.
+func UnmatchedRuleURLs(profile *config.BillingProfile, sources []config.Source) []string {
+	if profile == nil {
+		return nil
+	}
+	var out []string
+	for i := range profile.Rules {
+		rule := &profile.Rules[i]
+		if rule.URL == "*" {
+			continue
+		}
+		if len(matchSources(rule.URL, sources)) == 0 {
+			out = append(out, rule.URL)
+		}
+	}
+	return out
+}
+
 // matchSources returns the source names whose base_url matches pattern.
 // "*" matches every source (used as a catch-all default rule).
 func matchSources(pattern string, sources []config.Source) []string {

internal/billing/wildcard_test.go

@@ -289,3 +289,28 @@ func TestExplicitZeroModesKeepZeroTokenPrices(t *testing.T) {
 		}
 	}
 }
+
+// UnmatchedRuleURLs 是给调用方的"哪条规则写错了"清单：严格编译只会说
+// "compile failed"，而运维需要知道具体 URL；降级应用时也要能说明丢了什么。
+func TestUnmatchedRuleURLs(t *testing.T) {
+	sources := []config.Source{{Name: "mine", BaseURL: "https://mine.example.com/v1"}}
+	profile := &config.BillingProfile{
+		ID: "p",
+		Rules: []config.BillingRule{
+			{URL: "https://mine.example.com/v1", Mode: "free"},
+			{URL: "https://stale.example.com/v1", Mode: "free"},
+			{URL: "*", Mode: "token", Models: map[string]config.BillingToken{
+				"m": {Prompt: "1", Completion: "1"},
+			}},
+			{URL: "https://mine.example.com/v1/", Mode: "free"}, // 尾斜杠归一后匹配
+		},
+	}
+	got := UnmatchedRuleURLs(profile, sources)
+	if len(got) != 1 || got[0] != "https://stale.example.com/v1" {
+		t.Fatalf("unmatched = %v, want only the stale URL (wildcard and trailing-slash "+
+			"variants must not be reported)", got)
+	}
+	if nil != UnmatchedRuleURLs(nil, sources) {
+		t.Error("nil profile must yield nil")
+	}
+}