feat: add NovitaAI as LLM provider

Add NovitaAI as a first-class provider with dedicated model selection
flow, live pricing, and authoritative context length resolution.

- Register provider in PROVIDER_REGISTRY, HERMES_OVERLAYS, and all
  alias/label maps (ID: novita, aliases: novita-ai, novitaai)
- Add dedicated _model_flow_novita() with 3-tier model list fallback:
  Novita API → models.dev → static curated list
- Fetch live pricing from /v1/models with correct unit conversion
  (input_token_price_per_m is 0.0001 USD per Mtok)
- Add Novita-specific context length resolution (step 4b) in
  get_model_context_length(), prioritized over models.dev/OpenRouter
- Register api.novita.ai in _URL_TO_PROVIDER to prevent early return
  from the custom-endpoint code path
- Add models.dev mapping (novita → novita-ai)
- Add default auxiliary model (deepseek/deepseek-v3-0324)
- Add NOVITA_API_KEY to test isolation (conftest.py)
- Update docs: providers page, env vars reference, CLI reference,
  .env.example, README, and landing page

plugins/model-providers/novita/__init__.py

@@ -0,0 +1,27 @@
+"""NovitaAI provider profile."""
+
+from providers import register_provider
+from providers.base import ProviderProfile
+
+
+novita = ProviderProfile(
+    name="novita",
+    aliases=("novita-ai", "novitaai"),
+    display_name="NovitaAI",
+    description="NovitaAI — multi-model aggregator with pay-per-use pricing",
+    signup_url="https://novita.ai/settings/key-management",
+    env_vars=("NOVITA_API_KEY", "NOVITA_BASE_URL"),
+    base_url="https://api.novita.ai/openai/v1",
+    auth_type="api_key",
+    default_aux_model="deepseek/deepseek-v3-0324",
+    fallback_models=(
+        "moonshotai/kimi-k2.5",
+        "minimax/minimax-m2.7",
+        "zai-org/glm-5",
+        "deepseek/deepseek-v3-0324",
+        "deepseek/deepseek-r1-0528",
+        "qwen/qwen3-235b-a22b-fp8",
+    ),
+)
+
+register_provider(novita)

plugins/model-providers/novita/plugin.yaml

@@ -0,0 +1,5 @@
+name: novita-provider
+kind: model-provider
+version: 1.0.0
+description: NovitaAI multi-model aggregator
+author: Nous Research