fix(entity): close concurrency race + Unicode NFC/NFD split

[KailasMahavarkar]

Adversarial stress smoke (10 scenarios, 22+ assertions) found two production-relevant bugs in the resolver:

1. Concurrency race (HIGH severity for LLM-rate ingest)

resolve_mention() reads candidates, returns "no match" + fresh entity_id; caller issues CREATE NODE. Two threads racing on the same name both observe zero candidates → both mint distinct ids → N entities for one human.

Repro: 8 threads × 50 ingests of name "Bob" leaked 2-4 canonical Bobs per run.

Fix: new resolve_and_create_entity() wraps the read+write under a process-global lock + name→entity_id cache. Cache short-circuits the second concurrent caller without a NODES query, bypassing read-after-write visibility lag.

Result: 5 consecutive 8-thread × 50-mention runs all produce exactly 1 canonical entity.

2. NFC vs NFD Unicode split (MEDIUM)

"Müller" with composed ü (NFC, U+00FC) and decomposed ü (NFD, u + U+0308) normalized to mller vs muller because the regex strips the combining mark only AFTER NFD decomposition.

Fix: normalize_name NFKD-decomposes first; both encodings → muller.

bonsai_ingestor

Synthesizer uses resolve_and_create_entity so the entity write happens under the lock. Tests with gs=None still get a CREATE NODE for the entity inline (the wrapper isn't called).

Test plan

pytest tests/test_entity_resolver.py tests/test_bonsai_ingestor.py
-> 115 passed

pytest --tb=short -q ...
-> 1952 passed, 102 skipped

Stress smoke (/tmp/smoke_entity_stress.py, 10 scenarios):

• 1000 same-name single thread → 1 entity
• 500 distinct names → 500 entities, 41 ingests/s
• 8 threads × 50 same-name → 1 entity (was 2-4)
• 20 candidates → 2 ms resolver
• DSL injection survived
• Unicode/emoji names ingest
• NFC vs NFD Müller → both "muller"
• 50KB context OK
• 50 sessions × 200 mentions, 30 unique people → 30 entities, 216 ingests/s

Outstanding (separate work):

• Replay of same msg_id raises Node already exists: 'm1'. By-design CREATE semantics. Pipelines must dedupe msg_ids upstream or use UPSERT for idempotent retries.