feat: add Unicode-aware expression indexes for German umlaut search (#261)

SQLite's LOWER() only handles ASCII — LOWER('Ä') returns 'Ä', not 'ä'.
Add expression indexes using REPLACE(REPLACE(REPLACE(LOWER(...), 'Ä', 'ä'),
'Ö', 'ö'), 'Ü', 'ü')) for all columns used in ahb-tabellen search.

These indexes enable the LIKE optimization for prefix queries (startsWith)
when the search code uses the matching REPLACE expression. Substring queries
(%pattern%) always do full scans regardless of indexes.

Related: Hochfrequenz/ahb-tabellen#790

Co-authored-by: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: hf-kklein

src/fundamend/sqlmodels/materialize_ahb_view.sql

@@ -636,14 +636,17 @@ CREATE INDEX idx_hierarchy_gueltig_von ON ahb_hierarchy_materialized (gueltig_vo
 CREATE INDEX idx_hierarchy_gueltig_bis ON ahb_hierarchy_materialized (gueltig_bis);
 CREATE INDEX idx_hierarchy_beschreibung ON ahb_hierarchy_materialized (beschreibung);
 CREATE INDEX idx_hierarchy_beschreibung_lower ON ahb_hierarchy_materialized (lower(beschreibung));
+CREATE INDEX idx_hierarchy_beschreibung_unicode_lower ON ahb_hierarchy_materialized (REPLACE(REPLACE(REPLACE(LOWER(beschreibung), 'Ä', 'ä'), 'Ö', 'ö'), 'Ü', 'ü'));
 CREATE INDEX idx_hierarchy_kommunikationsrichtungen ON ahb_hierarchy_materialized (kommunikationsrichtungen);
 CREATE INDEX idx_hierarchy_edifact_format_version ON ahb_hierarchy_materialized (edifact_format_version);
 CREATE INDEX idx_hierarchy_segmentgroup_id ON ahb_hierarchy_materialized (segmentgroup_id);
 CREATE INDEX idx_hierarchy_segmentgroup_id_lower ON ahb_hierarchy_materialized (lower(segmentgroup_id));
+CREATE INDEX idx_hierarchy_segmentgroup_id_unicode_lower ON ahb_hierarchy_materialized (REPLACE(REPLACE(REPLACE(LOWER(segmentgroup_id), 'Ä', 'ä'), 'Ö', 'ö'), 'Ü', 'ü'));
 CREATE INDEX idx_hierarchy_segmentgroup_name ON ahb_hierarchy_materialized (segmentgroup_name);
 CREATE INDEX idx_hierarchy_segmentgroup_position ON ahb_hierarchy_materialized (segmentgroup_position);
 CREATE INDEX idx_hierarchy_segment_id ON ahb_hierarchy_materialized (segment_id);
 CREATE INDEX idx_hierarchy_segment_id_lower ON ahb_hierarchy_materialized (lower(segment_id));
+CREATE INDEX idx_hierarchy_segment_id_unicode_lower ON ahb_hierarchy_materialized (REPLACE(REPLACE(REPLACE(LOWER(segment_id), 'Ä', 'ä'), 'Ö', 'ö'), 'Ü', 'ü'));
 CREATE INDEX idx_hierarchy_segment_name ON ahb_hierarchy_materialized (segment_name);
 CREATE INDEX idx_hierarchy_segment_number ON ahb_hierarchy_materialized (segment_number);
 CREATE INDEX idx_hierarchy_segment_position ON ahb_hierarchy_materialized (segment_position);
@@ -652,15 +655,18 @@ CREATE INDEX idx_hierarchy_dataelementgroup_name ON ahb_hierarchy_materialized (
 CREATE INDEX idx_hierarchy_dataelementgroup_position ON ahb_hierarchy_materialized (dataelementgroup_position);
 CREATE INDEX idx_hierarchy_dataelement_id ON ahb_hierarchy_materialized (dataelement_id);
 CREATE INDEX idx_hierarchy_dataelement_id_lower ON ahb_hierarchy_materialized (lower(dataelement_id));
+CREATE INDEX idx_hierarchy_dataelement_id_unicode_lower ON ahb_hierarchy_materialized (REPLACE(REPLACE(REPLACE(LOWER(dataelement_id), 'Ä', 'ä'), 'Ö', 'ö'), 'Ü', 'ü'));
 CREATE INDEX idx_hierarchy_dataelement_name ON ahb_hierarchy_materialized (dataelement_name);
 CREATE INDEX idx_hierarchy_dataelement_position ON ahb_hierarchy_materialized (dataelement_position);
 CREATE INDEX idx_hierarchy_dataelement_ahb_status ON ahb_hierarchy_materialized (dataelement_ahb_status);
 CREATE INDEX idx_hierarchy_code_id ON ahb_hierarchy_materialized (code_id);
 CREATE INDEX idx_hierarchy_code_name ON ahb_hierarchy_materialized (code_name);
 CREATE INDEX idx_hierarchy_code_description ON ahb_hierarchy_materialized (code_description);
 CREATE INDEX idx_hierarchy_code_description_lower ON ahb_hierarchy_materialized (lower(code_description));
+CREATE INDEX idx_hierarchy_code_description_unicode_lower ON ahb_hierarchy_materialized (REPLACE(REPLACE(REPLACE(LOWER(code_description), 'Ä', 'ä'), 'Ö', 'ö'), 'Ü', 'ü'));
 CREATE INDEX idx_hierarchy_code_value ON ahb_hierarchy_materialized (code_value);
 CREATE INDEX idx_hierarchy_code_value_lower ON ahb_hierarchy_materialized (lower(code_value));
+CREATE INDEX idx_hierarchy_code_value_unicode_lower ON ahb_hierarchy_materialized (REPLACE(REPLACE(REPLACE(LOWER(code_value), 'Ä', 'ä'), 'Ö', 'ö'), 'Ü', 'ü'));
 CREATE INDEX idx_hierarchy_code_ahb_status ON ahb_hierarchy_materialized (code_ahb_status);
 CREATE INDEX idx_hierarchy_code_position ON ahb_hierarchy_materialized (code_position);
 CREATE INDEX idx_hierarchy_path ON ahb_hierarchy_materialized (path);
@@ -674,8 +680,10 @@ CREATE INDEX idx_ahb_tabellen_filter2 ON ahb_hierarchy_materialized (type) WHERE
 -- indexes for computed columns for v_ahbtabellen
 CREATE INDEX idx_line_ahb_status ON ahb_hierarchy_materialized (line_ahb_status);
 CREATE INDEX idx_line_ahb_status_lower ON ahb_hierarchy_materialized (lower(line_ahb_status));
+CREATE INDEX idx_line_ahb_status_unicode_lower ON ahb_hierarchy_materialized (REPLACE(REPLACE(REPLACE(LOWER(line_ahb_status), 'Ä', 'ä'), 'Ö', 'ö'), 'Ü', 'ü'));
 CREATE INDEX idx_line_name ON ahb_hierarchy_materialized (line_name);
 CREATE INDEX idx_line_name_lower ON ahb_hierarchy_materialized (lower(line_name));
+CREATE INDEX idx_line_name_unicode_lower ON ahb_hierarchy_materialized (REPLACE(REPLACE(REPLACE(LOWER(line_name), 'Ä', 'ä'), 'Ö', 'ö'), 'Ü', 'ü'));
 CREATE INDEX idx_hierarchy_sort_path_per_ahb ON ahb_hierarchy_materialized (sort_path, pruefidentifikator, edifact_format_version);
 
 -- Fallback: append occurrence counter '#N' to any id_paths that are still not unique after qualifier injection.