fix: 8 pipeline bugs from deep audit (graph dedup, feedback wiring, decay)

[varun29ankuS]

Summary

• Graph dedup: Removed duplicate graph processing from remember() — only process_experience_into_graph() at the handler layer creates entities/edges now, preventing inflated mention_counts and spurious edge strengthening
• Feedback → graph wiring: When feedback confirms a memory was helpful, its episode's entity edges are now strengthened via strengthen_episode_entity_edges() (Hebbian: what fires together wires together)
• Context pattern detection: Wired detect_context_pattern(), apply_context_pattern_signals(), and set_previous_context() into the proactive_context handler — repetition and topic-change signals now modulate feedback
• Full graph decay: apply_decay() now runs on heavy maintenance cycles (every 6 hours) alongside lazy pruning, ensuring no edge escapes time-based weakening
• Upsert episode cleanup: delete_episode() is called before process_experience_into_graph() on updates, preventing stale edges from prior versions
• Batch dedup: Content-hash dedup rejects duplicate items within the same batch
• Relevance EMA decay: Fixed relevance.rs using raw .ema instead of .ema_with_decay() — stale scores were shifting results by ~0.10
• Dead code removal: Removed stability_with_decay() and its unused DECAY_STABILITY_HALF_LIFE_DAYS constant
• Crash fix: Strip system noise (<task-notification>, <system-reminder> XML) at proactive_context handler entry in both Rust and MCP TypeScript, preventing BM25/embedding overload from multi-KB XML scaffolding

Test plan

• cargo check + cargo clippy — zero errors, zero new warnings
• Single remember → recall verified
• Batch remember with duplicates: 3 in → 2 created, 1 rejected
• Upsert create (v1) + update (v2) with was_update: true
• Proactive context with previous_response → feedback loop fires
• Repeated context triggers context pattern detection + repetition penalty
• Relevance endpoint responds without errors