feat(agent): wire MiniMax-M2.7 for minimax-oauth provider

Wire MiniMax-M2.7 and MiniMax-M2.7-highspeed into the model catalog,
CLI model picker, and agent auxiliary/metadata subsystems.

Changes:
- hermes_cli/models.py:
  - Add 'minimax-oauth' to _PROVIDER_MODELS with MiniMax-M2.7 and
    MiniMax-M2.7-highspeed
  - Add ProviderEntry('minimax-oauth', 'MiniMax (OAuth)', ...) to
    CANONICAL_PROVIDERS near existing minimax entries
  - Add aliases: minimax-portal, minimax-global, minimax_oauth in
    _PROVIDER_ALIASES
- hermes_cli/main.py:
  - Add 'minimax-oauth' to provider_labels dict
  - Insert 'minimax-oauth' into providers list in
    select_provider_and_model() near the other minimax entries
  - Add 'minimax-oauth' to --provider argparse choices
  - Add _model_flow_minimax_oauth() function: ensures login via
    _login_minimax_oauth(), resolves runtime credentials, prompts for
    model selection, saves model choice and config
  - Add dispatch elif branch for selected_provider == 'minimax-oauth'
- agent/auxiliary_client.py:
  - Add 'minimax-oauth': 'MiniMax-M2.7-highspeed' to
    _API_KEY_PROVIDER_AUX_MODELS
  - Add 'minimax-oauth' to _ANTHROPIC_COMPAT_PROVIDERS set
- agent/model_metadata.py:
  - Add 'minimax-oauth' to _PROVIDER_PREFIXES frozenset
  - MiniMax-M2.7 context length (200_000) already covered by the
    existing 'minimax' substring match in DEFAULT_CONTEXT_LENGTHS

hermes_cli/models.py

@@ -288,6 +288,10 @@ _PROVIDER_MODELS: dict[str, list[str]] = {
         "MiniMax-M2.1",
         "MiniMax-M2",
     ],
+    "minimax-oauth": [
+        "MiniMax-M2.7",
+        "MiniMax-M2.7-highspeed",
+    ],
     "minimax-cn": [
         "MiniMax-M2.7",
         "MiniMax-M2.5",
@@ -788,6 +792,7 @@ CANONICAL_PROVIDERS: list[ProviderEntry] = [
     ProviderEntry("kimi-coding-cn", "Kimi / Moonshot (China)",  "Kimi / Moonshot China (Moonshot CN direct API)"),
     ProviderEntry("stepfun",        "StepFun Step Plan",       "StepFun Step Plan (agent/coding models via Step Plan API)"),
     ProviderEntry("minimax",        "MiniMax",                  "MiniMax (global direct API)"),
+    ProviderEntry("minimax-oauth",  "MiniMax (OAuth)",          "MiniMax via OAuth browser login (Coding Plan, minimax.io)"),
     ProviderEntry("minimax-cn",     "MiniMax (China)",          "MiniMax China (domestic direct API)"),
     ProviderEntry("alibaba",        "Alibaba Cloud (DashScope)","Alibaba Cloud / DashScope Coding (Qwen + multi-provider)"),
     ProviderEntry("ollama-cloud",   "Ollama Cloud",             "Ollama Cloud (cloud-hosted open models — ollama.com)"),
@@ -831,6 +836,9 @@ _PROVIDER_ALIASES = {
     "gmicloud": "gmi",
     "minimax-china": "minimax-cn",
     "minimax_cn": "minimax-cn",
+    "minimax-portal": "minimax-oauth",
+    "minimax-global": "minimax-oauth",
+    "minimax_oauth": "minimax-oauth",
     "claude": "anthropic",
     "claude-code": "anthropic",
     "deep-seek": "deepseek",