chore: EXTRACTED_DIR marker cleanup + log rotation + dead code removal

[buildingjoshbetter]

Cleanup items from PR #315 review

1. EXTRACTED_DIR unbounded growth

~/.truememory/extracted/ accumulates one marker file per session_id forever. No TTL, no pruning.

• Add cleanup: delete markers >30 days old (checked on write or session_start)

2. Log file accumulation

~/.truememory/logs/ accumulates per-session log files from backlog drains. No rotation.

• Add cleanup: delete logs >7 days old

3. Dead code in _shared.py

should_extract() and mark_extracted() are no longer called after PR #315 removed incremental extraction from UserPromptSubmit.

• Remove both functions

4. TRUEMEMORY_INCREMENTAL_INTERVAL env var deprecated

This env var no longer does anything. Should be documented or logged as deprecated.

Found by: Rustle the Feathers adversarial review + codebase explorer

[buildingjoshbetter]

Status update (2026-05-15):

Items 3 and 4 are already resolved:

• ✅ Dead code should_extract() and mark_extracted() — removed in PR fix: ingestion pipeline — ghost recursion, double-ingest, backlog races #315
• ✅ TRUEMEMORY_INCREMENTAL_INTERVAL env var — no longer referenced anywhere

Items 1 and 2 remain (pure housekeeping):

• ⬜ EXTRACTED_DIR: 36,312 marker files (includes batch cleanup of extraction noise). Needs TTL-based pruning.
• ⬜ Log files: 1,058 files in ~/.truememory/logs/. Needs rotation.

Neither affects correctness or stability. P2 priority confirmed.