feat(providers): add Arcee AI as direct API provider

Adds Arcee AI as a standard direct provider (ARCEEAI_API_KEY) with
Trinity models: trinity-large-thinking, trinity-large-preview, trinity-mini.

Standard OpenAI-compatible provider checklist: auth.py, config.py,
models.py, main.py, providers.py, doctor.py, model_normalize.py,
model_metadata.py, setup.py, trajectory_compressor.py.

Based on PR #9274 by arthurbr11, simplified to a standard direct
provider without dual-endpoint OpenRouter routing.

agent/model_metadata.py

@@ -27,6 +27,7 @@ _PROVIDER_PREFIXES: frozenset[str] = frozenset({
     "opencode-zen", "opencode-go", "ai-gateway", "kilocode", "alibaba",
     "qwen-oauth",
     "xiaomi",
+    "arcee",
     "custom", "local",
     # Common aliases
     "google", "google-gemini", "google-ai-studio",
@@ -34,6 +35,7 @@ _PROVIDER_PREFIXES: frozenset[str] = frozenset({
     "github-models", "kimi", "moonshot", "kimi-cn", "moonshot-cn", "claude", "deep-seek",
     "opencode", "zen", "go", "vercel", "kilo", "dashscope", "aliyun", "qwen",
     "mimo", "xiaomi-mimo",
+    "arcee-ai", "arceeai",
     "qwen-portal",
 })
 
@@ -212,6 +214,7 @@ _URL_TO_PROVIDER: Dict[str, str] = {
     "api.moonshot.ai": "kimi-coding",
     "api.moonshot.cn": "kimi-coding-cn",
     "api.kimi.com": "kimi-coding",
+    "api.arcee.ai": "arcee",
     "api.minimax": "minimax",
     "dashscope.aliyuncs.com": "alibaba",
     "dashscope-intl.aliyuncs.com": "alibaba",