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

hermes_cli/providers.py

@@ -156,6 +156,11 @@ HERMES_OVERLAYS: Dict[str, HermesOverlay] = {
         is_aggregator=True,
         base_url_env_var="HF_BASE_URL",
     ),
+    "novita": HermesOverlay(
+        transport="openai_chat",
+        is_aggregator=True,
+        base_url_env_var="NOVITA_BASE_URL",
+    ),
     "xai": HermesOverlay(
         transport="codex_responses",
         base_url_override="https://api.x.ai/v1",
@@ -309,6 +314,10 @@ ALIASES: Dict[str, str] = {
     "hugging-face": "huggingface",
     "huggingface-hub": "huggingface",
 
+    # novita
+    "novita-ai": "novita",
+    "novitaai": "novita",
+
     # xiaomi
     "mimo": "xiaomi",
     "xiaomi-mimo": "xiaomi",