feat(memory): benchmarking harness, cost-sensitive store routing, goal-conditioned write gate

[bug-ops]

Summary

• research(memory): agentic memory benchmarking harness — hit rate, recall latency, compression ratio metrics (arXiv:2602.19320) #2419: Add .local/testing/bench-memory.py — stdlib-only Python benchmarking harness that seeds N facts into memory, runs M recall queries, and reports hit_rate, avg_recall_latency_ms, p50_ms, p99_ms, compression_ratio, interference_rate as JSON with CSV append for longitudinal tracking.
• research(memory): cost-sensitive store routing — select which memory store to query per query type (arXiv:2603.15658) #2444: Add cost-sensitive store routing to zeph-memory. New StoreRouter trait with HeuristicRouter, LlmRouter, and HybridRouter. Hybrid uses heuristic confidence and escalates to LLM only when ambiguous. New [memory.store_routing] config with routing_classifier_provider field. Deferred wiring tracked in feat(memory): wire StoreRoutingConfig into build_router() for cost-sensitive routing #2484.
• research(memory): CraniMem gated episodic+knowledge-graph memory — goal-conditioned write gate, scheduled consolidation (arXiv:2603.15642) #2408: Add CraniMem goal-conditioned write gate to admission control. goal_utility added as 6th AdmissionFactor. Disabled by default (goal_conditioned_write = false). Degenerate goal text guard (<10 chars) prevents arbitrary decisions on trivial input. New goal_utility_provider config field. Deferred wiring tracked in feat(memory): wire goal_text from agent context into remember() calls for CraniMem write gate #2483.

Closes #2419, #2444, #2408.

Test plan

• cargo nextest run --config-file .github/nextest.toml --workspace --features full --lib --bins — 7455 passed
• cargo +nightly fmt --check — clean
• cargo clippy --features full --workspace -- -D warnings — clean
• New unit tests: 10 added (router confidence, cosine_similarity, goal gate weight normalization)
• Deferred wiring: feat(memory): wire goal_text from agent context into remember() calls for CraniMem write gate #2483 (goal_text → remember()), feat(memory): wire StoreRoutingConfig into build_router() for cost-sensitive routing #2484 (StoreRoutingConfig → build_router())