fix: extract snapshot data from chunks, reduce ClickHouse log noise

- ChunkAccumulator now extracts inputBody/outputBody/inputHeaders/outputHeaders
  from ExecutionChunk.inputSnapshot/outputSnapshot instead of storing empty strings
- Set ClickHouse server log level to warning (was trace by default)
- Update CLAUDE.md to document Ed25519 key derivation

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

deploy/clickhouse.yaml

@@ -114,6 +114,11 @@ data:
   # Based on https://kb.altinity.com/altinity-kb-setup-and-maintenance/configure_clickhouse_for_low_mem_envs/
   low-memory.xml: |
     <clickhouse>
+        <!-- Reduce log verbosity (default is trace) -->
+        <logger>
+            <level>warning</level>
+        </logger>
+
         <!-- Let OS page out binary segments instead of pinning them in RAM -->
         <mlock_executable>false</mlock_executable>