fix: allow empty text field when doc_ids supplied to all tool APIs

dbnToolsString was called with required=true (default), so it aborted
before dbnToolsInjectDocContent could inject content from the doc picker.
Now passes required=false and validates after injection so doc-only
submissions work in timeline, redact, ask, and summarize.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

api/summarize.php

@@ -27,7 +27,7 @@ $emit = static function (string $event, array $payload): void {
 };
 
 try {
-    $text = dbnToolsInjectDocContent($input, dbnToolsString($input, 'text', 128000));
+    $text = dbnToolsInjectDocContent($input, dbnToolsString($input, 'text', 128000, false));
 
     if (mb_strlen(trim($text), 'UTF-8') < 50) {
         $emit('error', [