New post-turn memory feature with configurable extraction

What

• Three new environment variables control a new "post-turn memory" feature: CLAUDE_CODE_POST_TURN_MEMORY turns it on, CLAUDE_CODE_POST_TURN_MEMORY_CONFIG carries a JSON config (instruction, every_n_turns from 1-100 default 5, max_turns from 1-8 default 4, idle_flush_s from 0-86400 default 120), and CLAUDE_CODE_POST_TURN_MEMORY_SYNC forces synchronous flushing (everyNTurns=1, idleFlushSeconds=0).
• The background memory-extraction task now supports a second mode, mcp, driven by these same env vars: instead of writing memory files, it calls a query using the configured instruction and supports idle-flush timers.
• Extraction activity is now logged to a new ccr_memory_extract event set that records the mode (mcp vs file), instead of only the previous memory_extract event.

Why This lets memory extraction run through an MCP-based memory server rather than always writing local memory files, with configurable frequency, turn limits, and idle-flush timing, and gives clearer telemetry on which mode was used.