feat: add Alibaba Cloud provider and Anthropic base_url override (#1673)

Add Alibaba Cloud (DashScope) as a first-class inference provider
using the Anthropic-compatible endpoint. This gives access to Qwen
models (qwen3.5-plus, qwen3-max, qwen3-coder-plus, etc.) through
the same api_mode as native Anthropic.

Also add ANTHROPIC_BASE_URL env var support so users can point the
Anthropic provider at any compatible endpoint.

Changes:
- auth.py: Add alibaba ProviderConfig + ANTHROPIC_BASE_URL on anthropic
- models.py: Add alibaba to catalog, labels, aliases (dashscope/aliyun/qwen), provider order
- runtime_provider.py: Add alibaba resolution (anthropic_messages api_mode) + ANTHROPIC_BASE_URL
- model_metadata.py: Add Qwen model context lengths (128K)
- config.py: Add DASHSCOPE_API_KEY, DASHSCOPE_BASE_URL, ANTHROPIC_BASE_URL env vars

Usage:
  hermes --provider alibaba --model qwen3.5-plus
  # or via aliases:
  hermes --provider qwen --model qwen3-max

agent/model_metadata.py

@@ -116,6 +116,14 @@ DEFAULT_CONTEXT_LENGTHS = {
     "kimi-k2": 262144,
     "qwen3-coder": 32768,
     "big-pickle": 128000,
+    # Alibaba Cloud / DashScope Qwen models
+    "qwen3.5-plus": 131072,
+    "qwen3-max": 131072,
+    "qwen3-coder-plus": 131072,
+    "qwen3-coder-next": 131072,
+    "qwen-plus-latest": 131072,
+    "qwen3.5-flash": 131072,
+    "qwen-vl-max": 32768,
 }