feat(memory): HeLa-Mem spreading activation retrieval and query-bias tracing

[bug-ops]

Summary

• feat(memory): HeLa-Mem spreading activation retrieval #3346 — Implements HL-F5 spreading activation retrieval for HeLa-Mem: BFS from top-1 ANN anchor with multiplicative path weights, cosine clamping to [0,1], per-step circuit breaker, Hebbian reinforcement on traversed edges, dim-probe at startup, ANN fallback when anchor has no edges. Opt-in via [memory.hebbian] spreading_activation = false (zero-change invariant preserved).
• feat(memory): add tracing to apply_query_bias and profile_centroid_cached for observability #3379 — Adds tracing::info_span! and structured debug! events to apply_query_bias() and profile_centroid_cached(): all four skip branches (disabled, not_first_person, no_centroid, dim_mismatch), apply branch with centroid dim and weight, and three centroid branches (computed, cache hit with TTL, stale).

New public surface

• graph::activation::{HelaFact, HelaSpreadParams, hela_spreading_recall}
• VectorStore::get_points default trait method + Qdrant implementation
• EmbeddingStore::get_vectors_from_collection
• GraphStore::qdrant_point_ids_for_entities
• SemanticMemory::with_hebbian_spread + recall_graph_hela in semantic::recall
• Config migration step 31b for four new [memory.hebbian] fields

Test plan

• cargo nextest run --config-file .github/nextest.toml -p zeph-memory -p zeph-config --lib --no-fail-fast — 1546 unit tests pass
• cargo +nightly fmt --check -p zeph-memory -p zeph-config — clean
• cargo clippy -p zeph-memory -p zeph-config -- -D warnings — clean
• Integration tests in crates/zeph-memory/tests/hela_spreading_activation.rs — require Qdrant container, marked #[ignore]
• Coverage-status rows added for hela-mem-spread and query-bias-tracing (status: Untested)
• Playbook at .local/testing/playbooks/hela-mem-spreading.md

Closes #3346, #3379