Name the setting and value when a size setting does not parse (closes #429)

A non-numeric chunk_size or blob_size_limit failed with an error that named neither the setting nor the value. Every size setting now fails at load with its name and the quoted value, for example chunk_size: "banana" is not a size; use a number of bytes or a unit such as 10MB. A value too large for a size says so, with the setting name.

Model: opus-5-5

internal/config/config.go

@@ -290,7 +290,8 @@ func Load(path string) (*Config, error) {
 }
 
 // Parse reads YAML config data as Load does, without validating it. It
-// refuses a key that no setting has, applies default values for optional
+// refuses a key that no setting has and a size setting whose value is not a
+// size, naming the setting. It applies default values for optional
 // fields, fills in ${...} references using smartconfig, and expands ~ in
 // paths.
 func Parse(data []byte) (*Config, error) {
@@ -315,8 +316,9 @@ func Parse(data []byte) (*Config, error) {
 		return nil, fmt.Errorf("failed to load config file: %w", err)
 	}
 
-	// A ${...} reference can bring in keys that are not in the file.
-	err = checkFilledKeys(sc.Data())
+	// A ${...} reference can bring in keys that are not in the file, and
+	// is the value of a size setting only once it is filled in.
+	err = checkFilledConfig(sc.Data())
 	if err != nil {
 		return nil, err
 	}