feat(01-01): add WriteBuffer, repository interfaces, and config classes

- WriteBuffer<T> with offer/offerBatch/drain and backpressure (all tests green)
- ExecutionRepository, DiagramRepository, MetricsRepository interfaces
- MetricsSnapshot record for agent metrics data
- IngestionConfig for buffer-capacity/batch-size/flush-interval-ms properties
- ClickHouseConfig exposing JdbcTemplate bean

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

cameleer3-server-app/src/main/java/com/cameleer3/server/app/config/ClickHouseConfig.java

@@ -0,0 +1,22 @@
+package com.cameleer3.server.app.config;
+
+import org.springframework.context.annotation.Bean;
+import org.springframework.context.annotation.Configuration;
+import org.springframework.jdbc.core.JdbcTemplate;
+
+import javax.sql.DataSource;
+
+/**
+ * ClickHouse configuration.
+ * <p>
+ * Spring Boot auto-configures the DataSource from {@code spring.datasource.*} properties.
+ * This class exposes a JdbcTemplate bean for repository implementations.
+ */
+@Configuration
+public class ClickHouseConfig {
+
+    @Bean
+    public JdbcTemplate jdbcTemplate(DataSource dataSource) {
+        return new JdbcTemplate(dataSource);
+    }
+}

cameleer3-server-app/src/main/java/com/cameleer3/server/app/config/IngestionConfig.java

@@ -0,0 +1,41 @@
+package com.cameleer3.server.app.config;
+
+import org.springframework.boot.context.properties.ConfigurationProperties;
+import org.springframework.context.annotation.Configuration;
+
+/**
+ * Configuration properties for the ingestion write buffer.
+ * Bound from the {@code ingestion.*} namespace in application.yml.
+ */
+@Configuration
+@ConfigurationProperties(prefix = "ingestion")
+public class IngestionConfig {
+
+    private int bufferCapacity = 50_000;
+    private int batchSize = 5_000;
+    private long flushIntervalMs = 1_000;
+
+    public int getBufferCapacity() {
+        return bufferCapacity;
+    }
+
+    public void setBufferCapacity(int bufferCapacity) {
+        this.bufferCapacity = bufferCapacity;
+    }
+
+    public int getBatchSize() {
+        return batchSize;
+    }
+
+    public void setBatchSize(int batchSize) {
+        this.batchSize = batchSize;
+    }
+
+    public long getFlushIntervalMs() {
+        return flushIntervalMs;
+    }
+
+    public void setFlushIntervalMs(long flushIntervalMs) {
+        this.flushIntervalMs = flushIntervalMs;
+    }
+}