chore(memory): Phase 4 — Remove programmatic extraction and evaluate compaction removal

[platypusrex]

Summary

Clean up old code once OM v2 is proven. Remove programmatic extraction layer (PR #70), evaluate whether compaction code should be removed entirely.

Parent: #69
Depends on: Phase 1-3 proven in real usage

Scope

Delete

• src/memory/extractors.ts — Replaced by Observer
• src/memory/working-memory.ts — Replaced by Observer
• tests/test-memory.ts — Replaced by new test files
• tests/test-memory-integration.ts — Replaced by new test files

Evaluate

• src/agent/compaction.ts — Remove entirely if OM v2 is the sole context management strategy. Keep if we want a fallback.
• OBSERVATIONAL_MEMORY_PLAN.md — Archive or remove (replaced by V2 plan)

Update

• Remove unused imports and dead code paths referencing old observation system
• AGENTS.md if needed

Acceptance Criteria

• Old programmatic extraction code removed
• Old test files removed
• Decision made on compaction.ts (remove or keep as fallback)
• No dead imports or unused code paths
• All remaining tests pass