[proxy] Match dated Anthropic model ids against their undated form

shared/llm normalizes Bedrock and Vertex model ids so both sides of the
routing and pricing contract compare equal, but nothing did the same for a
first-party Anthropic id. A client pinning "claude-sonnet-4-5-20250929"
against a record registered as "claude-sonnet-4-5" denied as not-routable,
and where a catch-all route carried it through, the price lookup missed and
the request recorded no cost.

Add NormalizeAnthropicModel beside the existing two and consult it after an
exact match fails in the router's claim check, the pricing table, and the
per-record price map. Exact matches still win, so an operator who registers
two dated releases of the same family keeps them distinct.

shared/llm/model_test.go

@@ -34,3 +34,21 @@ func TestNormalizeVertexModel(t *testing.T) {
 		require.Equal(t, want, NormalizeVertexModel(in), "normalize %q", in)
 	}
 }
+
+func TestNormalizeAnthropicModel(t *testing.T) {
+	cases := map[string]string{
+		"claude-sonnet-4-5-20250929": "claude-sonnet-4-5",
+		"claude-3-5-haiku-20241022":  "claude-3-5-haiku",
+		"claude-sonnet-5":            "claude-sonnet-5",
+		"claude-opus-4-8":            "claude-opus-4-8",
+		// Other vendors' ids must survive untouched: none of them end in
+		// eight consecutive digits.
+		"gpt-4o":                     "gpt-4o",
+		"gpt-4o-2024-08-06":          "gpt-4o-2024-08-06",
+		"anthropic.claude-haiku-4-5": "anthropic.claude-haiku-4-5",
+		"":                           "",
+	}
+	for in, want := range cases {
+		require.Equal(t, want, NormalizeAnthropicModel(in), "normalize %q", in)
+	}
+}