Use youtube-transcript-api library with Playwright fallback for YouTube transcripts

Replace Jsoup-based approach with io.github.thoroldvix:youtube-transcript-api
as primary method (supports manual/generated captions, language priority).
Playwright head mode kept as fallback when API fails.

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

sundol-backend/pom.xml

@@ -104,6 +104,13 @@
             <version>1.18.3</version>
         </dependency>
 
+        <!-- YouTube Transcript API -->
+        <dependency>
+            <groupId>io.github.thoroldvix</groupId>
+            <artifactId>youtube-transcript-api</artifactId>
+            <version>0.4.0</version>
+        </dependency>
+
         <!-- Playwright (headless browser, driver-bundle includes node runtime) -->
         <dependency>
             <groupId>com.microsoft.playwright</groupId>