feat: add OpenRouter provider with full dispatch wiring

[ghshhf]

Adds OpenRouter as a first-class provider (closes the openrouter support request, e.g. #274).

OpenRouter is an OpenAI-compatible gateway to hundreds of models. This PR:

• adds scrapegraphai/models/openrouter.py (ChatOpenAI wrapper, base URL https://openrouter.ai/api/v1)
• registers it in models/__init__.py and helpers/models_tokens.py
• wires it into graphs/abstract_graph._create_llm (adds openrouter to known_providers and the dispatch branch) so model: "openrouter/<model>" actually resolves. Without this wiring the provider class is never instantiated (the same gap left by the open Atlas Cloud PR Add Atlas Cloud OpenAI-compatible model wrapper #1104).
• adds tests/test_openrouter_model.py mirroring the Atlas Cloud test

Usage:

graph_config = {"llm": {"model": "openrouter/anthropic/claude-3.5-sonnet", "api_key": OR_KEY}, ...}

Low risk: additive, mirrors the existing DeepSeek/OneApi pattern, and falls back to 8192 tokens if a model is not in the token table.