fix: global search case-insensitive + keyboard layout swap

Unified search normalization across InternalLinkPicker and GlobalSearch:

1. GlobalSearch.svelte: multi-variant search (same as InternalLinkPicker)
   - expandKeyboardVariants() for RU/EN layout swap
   - Parallel Search queries with dedup by type+nodeId+targetId+title
   - 180ms debounce preserved

2. Backend: fix LOWER() in SQL for links/actions
   - Replace LOWER(column) LIKE with lowercased columns (title_lower, url_lower, etc.)
   - Migration 020: add lowercased columns + indexes for links and actions
   - BackfillLinksLower() + BackfillActionsLower() in storage.go
   - Update INSERT in bindings_links.go and action.go to populate lowercased columns

3. FTS5 search: Unicode case-insensitive
   - Index lowercased title/content/tags in search_index
   - sanitizeFTS() now lowercases query before MATCH
   - RebuildFTS() called after migrations

4. Case-insensitive search for nodes (already done in previous commit, verified):
   - title_lower column with Go strings.ToLower
   - Search() queries title_lower with lowercased query

All test suites PASS, full build OK.

internal/core/actions/action.go

@@ -88,11 +88,13 @@ func (s *Service) Create(nodeID, kind, title, command, workingDir, url string, a
 
 	_, err := s.db.Exec(
 		`INSERT INTO actions (id,node_id,title,kind,command,args_json,working_dir,url,
-			confirm_required,capture_output,created_at,updated_at)
-		 VALUES (?,?,?,?,?,?,?,?,?,?,?,?)`,
+			confirm_required,capture_output,created_at,updated_at,
+			title_lower,kind_lower,url_lower,command_lower)
+		 VALUES (?,?,?,?,?,?,?,?,?,?,?,?,?,?,?,?)`,
 		rec.ID, rec.NodeID, rec.Title, rec.Kind, rec.Command, string(argsJSON),
 		rec.WorkingDir, rec.URL, boolInt(rec.ConfirmRequired), boolInt(rec.CaptureOutput),
 		rec.CreatedAt.Format(time.RFC3339), rec.UpdatedAt.Format(time.RFC3339),
+		strings.ToLower(rec.Title), strings.ToLower(rec.Kind), strings.ToLower(rec.URL), strings.ToLower(rec.Command),
 	)
 	if err != nil {
 		return nil, err