Lifecycle Phase 4 (Daily Use) + synthetic data generator

[CalebisGross]

Summary

Implement the daily usage phase and the synthetic memory data generator that powers it and later phases.

Synthetic Data Generator (data.go)

• Catalogs of realistic memories by type: decisions, errors, insights, learnings
• Source distribution: 30% MCP, 50% filesystem/terminal noise, 20% clipboard
• Repeated topics for association testing
• Feedback events (helpful, partial, irrelevant ratings)
• Deterministic via fixed seed

Phase 4: Daily Use (Days 3-14)

• Generate 200-300 memories across 12 simulated "days"
• Advance SimClock by ~1 day between batches
• Encode + episode after each "day"
• Write retrieval feedback records
• Assert:
  • Associations created (count > 0)
  • Access counts increment on retrieval
  • Feedback scores recorded correctly
  • Hebbian strengthening: associations between co-retrieved memories strengthened

Test plan

• ./bin/mnemonic lifecycle-test --phase=daily passes all assertions
• Data generator produces deterministic output across runs

Part of #248