feat(demo): add collapsible log panel with vertical tab

Implements expandable log panel as vertical side tab on right edge:

- LogEntry record with Level (INFO/DEBUG/WARN/ERROR) and Category (SYS/CACHE/RAG/LLM/PDF)
- EventLogger service with thread-safe CopyOnWriteArrayList, MAX_ENTRIES=500
- LogPanel with vertical 'LOG' tab + count badge, horizontal slide-out to 400px
- Dark theme with monospace font, color-coded log levels
- Logs: queries, cache hits/misses, PDF loading, retrieval timing, Redis connection
- Click tab to toggle expanded/collapsed state

Author: bsbodden

demos/rag-multimodal/src/main/java/com/redis/vl/demo/rag/model/LogEntry.java

@@ -0,0 +1,106 @@
+package com.redis.vl.demo.rag.model;
+
+import java.time.Instant;
+import java.time.ZoneId;
+import java.time.format.DateTimeFormatter;
+
+/**
+ * Represents a log entry in the application event log.
+ *
+ * @param timestamp When the event occurred
+ * @param level Log level (INFO, DEBUG, WARN, ERROR)
+ * @param category Event category (SYSTEM, CACHE, RETRIEVAL, LLM)
+ * @param message Human-readable message
+ */
+public record LogEntry(Instant timestamp, Level level, Category category, String message) {
+
+  private static final DateTimeFormatter TIME_FORMAT =
+      DateTimeFormatter.ofPattern("HH:mm:ss.SSS").withZone(ZoneId.systemDefault());
+
+  public enum Level {
+    INFO,
+    DEBUG,
+    WARN,
+    ERROR
+  }
+
+  public enum Category {
+    SYSTEM("SYS"),
+    CACHE("CACHE"),
+    RETRIEVAL("RAG"),
+    LLM("LLM"),
+    PDF("PDF");
+
+    private final String shortName;
+
+    Category(String shortName) {
+      this.shortName = shortName;
+    }
+
+    public String getShortName() {
+      return shortName;
+    }
+  }
+
+  /**
+   * Creates an INFO level log entry.
+   *
+   * @param category Event category
+   * @param message Log message
+   * @return New log entry
+   */
+  public static LogEntry info(Category category, String message) {
+    return new LogEntry(Instant.now(), Level.INFO, category, message);
+  }
+
+  /**
+   * Creates a DEBUG level log entry.
+   *
+   * @param category Event category
+   * @param message Log message
+   * @return New log entry
+   */
+  public static LogEntry debug(Category category, String message) {
+    return new LogEntry(Instant.now(), Level.DEBUG, category, message);
+  }
+
+  /**
+   * Creates a WARN level log entry.
+   *
+   * @param category Event category
+   * @param message Log message
+   * @return New log entry
+   */
+  public static LogEntry warn(Category category, String message) {
+    return new LogEntry(Instant.now(), Level.WARN, category, message);
+  }
+
+  /**
+   * Creates an ERROR level log entry.
+   *
+   * @param category Event category
+   * @param message Log message
+   * @return New log entry
+   */
+  public static LogEntry error(Category category, String message) {
+    return new LogEntry(Instant.now(), Level.ERROR, category, message);
+  }
+
+  /**
+   * Formats the timestamp for display.
+   *
+   * @return Formatted time string
+   */
+  public String formattedTime() {
+    return TIME_FORMAT.format(timestamp);
+  }
+
+  /**
+   * Formats the full log entry for display.
+   *
+   * @return Formatted log string
+   */
+  public String formatted() {
+    return String.format("[%s] [%s] [%s] %s", formattedTime(), level, category.getShortName(), message);
+  }
+}

demos/rag-multimodal/src/main/java/com/redis/vl/demo/rag/service/EventLogger.java

@@ -0,0 +1,123 @@
+package com.redis.vl.demo.rag.service;
+
+import com.redis.vl.demo.rag.model.LogEntry;
+import com.redis.vl.demo.rag.model.LogEntry.Category;
+import java.util.ArrayList;
+import java.util.List;
+import java.util.concurrent.CopyOnWriteArrayList;
+import java.util.function.Consumer;
+
+/**
+ * Centralized event logger for the RAG demo application.
+ *
+ * <p>Collects application events and notifies registered listeners.
+ * Thread-safe for use from multiple threads (UI thread, background executor).
+ */
+public class EventLogger {
+
+  private static final int MAX_ENTRIES = 500;
+
+  private final List<LogEntry> entries = new CopyOnWriteArrayList<>();
+  private final List<Consumer<LogEntry>> listeners = new CopyOnWriteArrayList<>();
+
+  /**
+   * Logs an INFO event.
+   *
+   * @param category Event category
+   * @param message Log message
+   */
+  public void info(Category category, String message) {
+    log(LogEntry.info(category, message));
+  }
+
+  /**
+   * Logs a DEBUG event.
+   *
+   * @param category Event category
+   * @param message Log message
+   */
+  public void debug(Category category, String message) {
+    log(LogEntry.debug(category, message));
+  }
+
+  /**
+   * Logs a WARN event.
+   *
+   * @param category Event category
+   * @param message Log message
+   */
+  public void warn(Category category, String message) {
+    log(LogEntry.warn(category, message));
+  }
+
+  /**
+   * Logs an ERROR event.
+   *
+   * @param category Event category
+   * @param message Log message
+   */
+  public void error(Category category, String message) {
+    log(LogEntry.error(category, message));
+  }
+
+  /**
+   * Logs an entry and notifies all listeners.
+   *
+   * @param entry Log entry to add
+   */
+  public void log(LogEntry entry) {
+    entries.add(entry);
+
+    // Trim old entries if we exceed max
+    while (entries.size() > MAX_ENTRIES) {
+      entries.remove(0);
+    }
+
+    // Notify listeners
+    for (Consumer<LogEntry> listener : listeners) {
+      try {
+        listener.accept(entry);
+      } catch (Exception e) {
+        // Don't let listener errors break logging
+        System.err.println("EventLogger listener error: " + e.getMessage());
+      }
+    }
+
+    // Also print to console for debugging
+    System.out.println(entry.formatted());
+  }
+
+  /**
+   * Adds a listener to receive new log entries.
+   *
+   * @param listener Callback for new entries
+   */
+  public void addListener(Consumer<LogEntry> listener) {
+    listeners.add(listener);
+  }
+
+  /**
+   * Removes a listener.
+   *
+   * @param listener Listener to remove
+   */
+  public void removeListener(Consumer<LogEntry> listener) {
+    listeners.remove(listener);
+  }
+
+  /**
+   * Gets all log entries.
+   *
+   * @return Copy of all entries
+   */
+  public List<LogEntry> getEntries() {
+    return new ArrayList<>(entries);
+  }
+
+  /**
+   * Clears all log entries.
+   */
+  public void clear() {
+    entries.clear();
+  }
+}