fix(search): analyze Content queries on OpenSearch

Content is an analyzed text field, but a single-term KQL query on it was
compiled to a term query, which matches the raw value against the tokenized
content and never hits. "Content:https://opencloud.eu/" (tokenized to
[https, opencloud.eu, ...]) returned nothing; "Content:alan@" likewise.

Route full-text fields to match_phrase so the query is analyzed the same way
as the indexed content. Fixes the OpenSearch content-search acceptance
scenarios (contentSearch.feature search by different content types).

services/search/pkg/opensearch/internal/convert/kql_transpile.go

@@ -15,6 +15,18 @@ func TranspileKQLToOpenSearch(nodes []ast.Node) (osu.Builder, error) {
 	return kqlOpensearchTranspiler{}.Transpile(nodes)
 }
 
+// fullTextFields are analyzed (text) fields whose query value must be analyzed
+// the same way as the indexed content. Querying them with a term query would
+// match the raw, unanalyzed value against tokenized content and miss.
+var fullTextFields = map[string]struct{}{
+	"Content": {},
+}
+
+func isFullTextField(key string) bool {
+	_, ok := fullTextFields[key]
+	return ok
+}
+
 type kqlOpensearchTranspiler struct{}
 
 func (t kqlOpensearchTranspiler) Transpile(nodes []ast.Node) (osu.Builder, error) {
@@ -108,6 +120,11 @@ func (t kqlOpensearchTranspiler) toBuilder(node ast.Node) (osu.Builder, error) {
 		isSingleTerm := len(totalTerms) == 1
 		isMultiTerm := len(totalTerms) >= 1
 		switch {
+		case isFullTextField(node.Key):
+			// analyzed text fields must analyze the query too; a term query looks
+			// for the raw value and never matches tokenized content, e.g.
+			// "Content:https://opencloud.eu/" against the tokenized URL
+			return osu.NewMatchPhraseQuery(node.Key).Query(node.Value), nil
 		case isSingleTerm:
 			return osu.NewTermQuery[string](node.Key).Value(node.Value), nil
 		case isMultiTerm:

services/search/pkg/opensearch/internal/convert/kql_transpile_test.go

@@ -51,6 +51,17 @@ func TestTranspileKQLToOpenSearch(t *testing.T) {
 			},
 			Want: osu.NewMatchPhraseQuery("Name").Query(`open cloud`),
 		},
+		{
+			Name: "match-phrase query - full text Content field, single term",
+			Got: &ast.Ast{
+				Nodes: []ast.Node{
+					&ast.StringNode{Key: "Content", Value: "https://opencloud.eu/"},
+				},
+			},
+			// Content is analyzed, so even a single term must use match_phrase
+			// rather than a term query, which would not match tokenized content.
+			Want: osu.NewMatchPhraseQuery("Content").Query("https://opencloud.eu/"),
+		},
 		{
 			Name: "wildcard query - string node",
 			Got: &ast.Ast{