feat(comment-cards): 유튜브 videoId 파서 추가

watch/youtu.be/shorts/embed/순수ID 추출, 단위 테스트 포함

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

src/main/java/com/hlab/yanalyst/service/YoutubeVideoIdParser.java

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+package com.hlab.yanalyst.service;
+
+import java.util.regex.Pattern;
+import java.util.regex.Matcher;
+
+/** 유튜브 URL 또는 11자리 영상 ID에서 videoId를 추출한다. 실패 시 null. */
+public final class YoutubeVideoIdParser {
+
+    private static final Pattern BARE = Pattern.compile("^[A-Za-z0-9_-]{11}$");
+    private static final Pattern[] PATTERNS = {
+        Pattern.compile("[?&]v=([A-Za-z0-9_-]{11})"),
+        Pattern.compile("youtu\\.be/([A-Za-z0-9_-]{11})"),
+        Pattern.compile("/shorts/([A-Za-z0-9_-]{11})"),
+        Pattern.compile("/embed/([A-Za-z0-9_-]{11})"),
+    };
+
+    private YoutubeVideoIdParser() {}
+
+    public static String parse(String input) {
+        if (input == null) return null;
+        String s = input.trim();
+        if (s.isEmpty()) return null;
+        if (BARE.matcher(s).matches()) return s;
+        for (Pattern p : PATTERNS) {
+            Matcher m = p.matcher(s);
+            if (m.find()) return m.group(1);
+        }
+        return null;
+    }
+}

src/test/java/com/hlab/yanalyst/service/YoutubeVideoIdParserTest.java

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+package com.hlab.yanalyst.service;
+
+import org.junit.jupiter.api.Test;
+import static org.junit.jupiter.api.Assertions.*;
+
+class YoutubeVideoIdParserTest {
+
+    @Test
+    void parsesWatchUrl() {
+        assertEquals("dQw4w9WgXcQ",
+            YoutubeVideoIdParser.parse("https://www.youtube.com/watch?v=dQw4w9WgXcQ"));
+    }
+
+    @Test
+    void parsesWatchUrlWithExtraParams() {
+        assertEquals("dQw4w9WgXcQ",
+            YoutubeVideoIdParser.parse("https://www.youtube.com/watch?v=dQw4w9WgXcQ&t=42s&list=ABC"));
+    }
+
+    @Test
+    void parsesShortLink() {
+        assertEquals("dQw4w9WgXcQ",
+            YoutubeVideoIdParser.parse("https://youtu.be/dQw4w9WgXcQ?si=xyz"));
+    }
+
+    @Test
+    void parsesShortsLink() {
+        assertEquals("abc12345678",
+            YoutubeVideoIdParser.parse("https://www.youtube.com/shorts/abc12345678"));
+    }
+
+    @Test
+    void parsesBareId() {
+        assertEquals("dQw4w9WgXcQ", YoutubeVideoIdParser.parse("dQw4w9WgXcQ"));
+    }
+
+    @Test
+    void returnsNullForGarbage() {
+        assertNull(YoutubeVideoIdParser.parse("not a youtube link"));
+        assertNull(YoutubeVideoIdParser.parse(""));
+        assertNull(YoutubeVideoIdParser.parse(null));
+    }
+}