Add --until flag to crystal search for date range queries

[lesaai]

Summary

crystal search has --since (everything newer than X) but no --until. Need both for backfilling daily summaries.

Usage

crystal search "what happened" --since 2026-02-10 --until 2026-02-11

Returns only chunks from that date range. Required for generating historical daily summaries.

Where

• memory-crystal-private/src/core.ts (search function, SQL filter)
• memory-crystal-private/src/cli.ts (CLI flag)
• memory-crystal-private/src/mcp-server.ts (MCP tool parameter)
• memory-crystal-private/src/search-pipeline.ts (deep search filter)

Related

• #193 (multi-cadence summaries ... backfill requires date ranges)