feat(providers): add tencent-tokenhub provider support

Registers tencent-tokenhub (https://tokenhub.tencentmaas.com/v1) as a
new API-key provider with model tencent/hy3-preview (256K context).

- PROVIDER_REGISTRY entry + TOKENHUB_API_KEY / TOKENHUB_BASE_URL env vars
- Aliases: tencent, tokenhub, tencent-cloud, tencentmaas
- openai_chat transport with is_tokenhub branch for top-level
  reasoning_effort (Hy3 is a reasoning model)
- tencent/hy3-preview:free added to OpenRouter curated list
- 60+ tests (provider registry, aliases, runtime resolution,
  credentials, model catalog, URL mapping, context length)
- Docs: integrations/providers.md, environment-variables.md,
  model-catalog.json

Author: simonweng <simonweng@tencent.com>
Salvaged from PR #16860 onto current main (resolved conflicts with
#16935 Azure Anthropic env-var hint tests and the --provider choices=
list removal in chat_parser).

hermes_cli/models.py

@@ -44,6 +44,7 @@ OPENROUTER_MODELS: list[tuple[str, str]] = [
     ("openai/gpt-5.4-mini",             ""),
     ("xiaomi/mimo-v2.5-pro",             ""),
     ("xiaomi/mimo-v2.5",                 ""),
+    ("tencent/hy3-preview:free",         "free"),
     ("openai/gpt-5.3-codex",            ""),
     ("google/gemini-3-pro-image-preview", ""),
     ("google/gemini-3-flash-preview",   ""),
@@ -156,6 +157,7 @@ _PROVIDER_MODELS: dict[str, list[str]] = {
         "moonshotai/kimi-k2.6",
         "xiaomi/mimo-v2.5-pro",
         "xiaomi/mimo-v2.5",
+        "tencent/hy3-preview",
         "anthropic/claude-opus-4.7",
         "anthropic/claude-opus-4.6",
         "anthropic/claude-sonnet-4.6",
@@ -315,6 +317,9 @@ _PROVIDER_MODELS: dict[str, list[str]] = {
         "mimo-v2-omni",
         "mimo-v2-flash",
     ],
+    "tencent-tokenhub": [
+        "hy3-preview",
+    ],
     "arcee": [
         "trinity-large-thinking",
         "trinity-large-preview",
@@ -767,6 +772,7 @@ CANONICAL_PROVIDERS: list[ProviderEntry] = [
     ProviderEntry("anthropic",      "Anthropic",                "Anthropic (Claude models — API key or Claude Code)"),
     ProviderEntry("openai-codex",   "OpenAI Codex",             "OpenAI Codex"),
     ProviderEntry("xiaomi",         "Xiaomi MiMo",              "Xiaomi MiMo (MiMo-V2.5 and V2 models — pro, omni, flash)"),
+    ProviderEntry("tencent-tokenhub", "Tencent TokenHub",       "Tencent TokenHub (Hy3 Preview — direct API via tokenhub.tencentmaas.com)"),
     ProviderEntry("nvidia",         "NVIDIA NIM",               "NVIDIA NIM (Nemotron models — build.nvidia.com or local NIM)"),
     ProviderEntry("qwen-oauth",     "Qwen OAuth (Portal)",      "Qwen OAuth (reuses local Qwen CLI login)"),
     ProviderEntry("copilot",        "GitHub Copilot",           "GitHub Copilot (uses GITHUB_TOKEN or gh auth token)"),
@@ -849,6 +855,10 @@ _PROVIDER_ALIASES = {
     "huggingface-hub": "huggingface",
     "mimo": "xiaomi",
     "xiaomi-mimo": "xiaomi",
+    "tencent": "tencent-tokenhub",
+    "tokenhub": "tencent-tokenhub",
+    "tencent-cloud": "tencent-tokenhub",
+    "tencentmaas": "tencent-tokenhub",
     "aws": "bedrock",
     "aws-bedrock": "bedrock",
     "amazon-bedrock": "bedrock",