feat(search): add AttributeFilter record with key regex + wildcard pattern translation

cameleer-server-core/src/main/java/com/cameleer/server/core/search/AttributeFilter.java

@@ -0,0 +1,60 @@
+package com.cameleer.server.core.search;
+
+import java.util.regex.Pattern;
+
+/**
+ * Structured attribute filter for execution search.
+ * <p>
+ * Value semantics:
+ * <ul>
+ *   <li>{@code value == null} or blank -> key-exists check</li>
+ *   <li>{@code value} contains {@code *} -> wildcard match (translated to SQL LIKE pattern)</li>
+ *   <li>otherwise -> exact match</li>
+ * </ul>
+ * <p>
+ * Keys must match {@code ^[a-zA-Z0-9._-]+$} — they are later inlined into
+ * ClickHouse SQL via {@code JSONExtractString}, which does not accept a
+ * parameter placeholder for the JSON path. Values are always parameter-bound.
+ */
+public record AttributeFilter(String key, String value) {
+
+    private static final Pattern KEY_PATTERN = Pattern.compile("^[a-zA-Z0-9._-]+$");
+
+    public AttributeFilter {
+        if (key == null || !KEY_PATTERN.matcher(key).matches()) {
+            throw new IllegalArgumentException(
+                    "Invalid attribute key: must match " + KEY_PATTERN.pattern() + ", got: " + key);
+        }
+        if (value != null && value.isBlank()) {
+            value = null;
+        }
+    }
+
+    public boolean isKeyOnly() {
+        return value == null;
+    }
+
+    public boolean isWildcard() {
+        return value != null && value.indexOf('*') >= 0;
+    }
+
+    /**
+     * Returns a SQL LIKE pattern for wildcard matches with {@code %} / {@code _} / {@code \}
+     * in the source value escaped, or {@code null} for exact / key-only filters.
+     */
+    public String toLikePattern() {
+        if (!isWildcard()) return null;
+        StringBuilder sb = new StringBuilder(value.length() + 4);
+        for (int i = 0; i < value.length(); i++) {
+            char c = value.charAt(i);
+            switch (c) {
+                case '\\' -> sb.append("\\\\");
+                case '%' -> sb.append("\\%");
+                case '_' -> sb.append("\\_");
+                case '*' -> sb.append('%');
+                default -> sb.append(c);
+            }
+        }
+        return sb.toString();
+    }
+}

cameleer-server-core/src/test/java/com/cameleer/server/core/search/AttributeFilterTest.java

@@ -0,0 +1,61 @@
+package com.cameleer.server.core.search;
+
+import org.junit.jupiter.api.Test;
+
+import static org.assertj.core.api.Assertions.assertThat;
+import static org.assertj.core.api.Assertions.assertThatThrownBy;
+
+class AttributeFilterTest {
+
+    @Test
+    void keyOnly_blankValue_normalizesToNull() {
+        AttributeFilter f = new AttributeFilter("order", "");
+        assertThat(f.value()).isNull();
+        assertThat(f.isKeyOnly()).isTrue();
+        assertThat(f.isWildcard()).isFalse();
+    }
+
+    @Test
+    void keyOnly_nullValue_isKeyOnly() {
+        AttributeFilter f = new AttributeFilter("order", null);
+        assertThat(f.isKeyOnly()).isTrue();
+    }
+
+    @Test
+    void exactValue_isNotWildcard() {
+        AttributeFilter f = new AttributeFilter("order", "47");
+        assertThat(f.isKeyOnly()).isFalse();
+        assertThat(f.isWildcard()).isFalse();
+    }
+
+    @Test
+    void starInValue_isWildcard() {
+        AttributeFilter f = new AttributeFilter("order", "47*");
+        assertThat(f.isWildcard()).isTrue();
+    }
+
+    @Test
+    void invalidKey_throws() {
+        assertThatThrownBy(() -> new AttributeFilter("bad key", "x"))
+                .isInstanceOf(IllegalArgumentException.class)
+                .hasMessageContaining("attribute key");
+    }
+
+    @Test
+    void blankKey_throws() {
+        assertThatThrownBy(() -> new AttributeFilter(" ", null))
+                .isInstanceOf(IllegalArgumentException.class);
+    }
+
+    @Test
+    void wildcardPattern_escapesLikeMetaCharacters() {
+        AttributeFilter f = new AttributeFilter("order", "a_b%c\\d*");
+        assertThat(f.toLikePattern()).isEqualTo("a\\_b\\%c\\\\d%");
+    }
+
+    @Test
+    void exactValue_toLikePattern_returnsNull() {
+        AttributeFilter f = new AttributeFilter("order", "47");
+        assertThat(f.toLikePattern()).isNull();
+    }
+}