Updates in preparation for adding forecast sources.

internal/normalizers/doc.go

@@ -34,7 +34,7 @@
 //     as they do not define additional Normalizer types.
 //
 //  2. Provider-level shared helpers live under the provider directory:
-//     internal/normalizers/<provider>/
+//     internal/providers/<provider>/
 //
 //     Use this for provider-specific quirks that should be shared by BOTH sources
 //     and normalizers (time parsing, URL/unit invariants, ID normalization, etc.).
@@ -44,8 +44,6 @@
 //     - types.go        (provider JSON structs)
 //     - common.go       (provider-shared helpers)
 //     - mapping.go      (provider mapping logic)
-//     Use common.go only when you truly have “shared across multiple normalizers
-//     within this provider” helpers.
 //
 //  3. Cross-provider helpers live in:
 //     internal/normalizers/common/