fix: route OpenRouter-only providers through OpenRouter API (#38)

Providers without their own public API now use OpenRouter as their
base_url with OPENROUTER_API_KEY, making them testable and usable
when the user has an OpenRouter key configured.

- 20 OpenRouter-only providers: set base_url to openrouter.ai/api/v1
- morph: set correct official API (api.morphllm.com/v1)
- sync-pricing.py: default to OpenRouter routing for new providers

providers/meta-llama.toml

@@ -3,9 +3,9 @@
 [provider]
 id = "meta-llama"
 display_name = "Meta Llama"
-api_key_env = "META_LLAMA_API_KEY"
-base_url = ""
-key_required = false
+api_key_env = "OPENROUTER_API_KEY"
+base_url = "https://openrouter.ai/api/v1"
+key_required = true
 
 [[models]]
 id = "llama-3-70b-instruct"