Azure/Kimi models not routed correctly; DB overrides ignored by algorithm

[shroominic]

Two issues in the model routing algorithm:

1. Deployment-based providers (Azure, Kimi) whose models aren't discovered at runtime are skipped even if DB overrides exist for them.
2. Model deduplication doesn't account for provider identity, so overrides can be silently dropped.

Fix: include enabled DB overrides when the provider is known, and deduplicate by (model_id, provider_identity).

Files: `routstr/algorithm.py`, `routstr/upstream/azure.py`, `routstr/upstream/base.py`, `routstr/upstream/helpers.py`