feat: provider modules — ProviderProfile ABC, 33 providers, fetch_models, transport single-path

Introduces providers/ package — single source of truth for every
inference provider. Adding a simple api-key provider now requires one
providers/<name>.py file with zero edits anywhere else.

What this PR ships:
- providers/ package (ProviderProfile ABC + 33 profiles across 4 api_modes)
- ProviderProfile declarative fields: name, api_mode, aliases, display_name,
  env_vars, base_url, models_url, auth_type, fallback_models, hostname,
  default_headers, fixed_temperature, default_max_tokens, default_aux_model
- 4 overridable hooks: prepare_messages, build_extra_body,
  build_api_kwargs_extras, fetch_models
- chat_completions.build_kwargs: profile path via _build_kwargs_from_profile,
  legacy flag path retained for lmstudio/tencent-tokenhub (which have
  session-aware reasoning probing that doesn't map cleanly to hooks yet)
- run_agent.py: profile path for all registered providers; legacy path
  variable scoping fixed (all flags defined before branching)
- Auto-wires: auth.PROVIDER_REGISTRY, models.CANONICAL_PROVIDERS,
  doctor health checks, config.OPTIONAL_ENV_VARS, model_metadata._URL_TO_PROVIDER
- GeminiProfile: thinking_config translation (native + openai-compat nested)
- New tests/providers/ (79 tests covering profile declarations, transport
  parity, hook overrides, e2e kwargs assembly)

Deltas vs original PR (salvaged onto current main):
- Added profiles: alibaba-coding-plan, azure-foundry, minimax-oauth
  (were added to main since original PR)
- Skipped profiles: lmstudio, tencent-tokenhub stay on legacy path (their
  reasoning_effort probing has no clean hook equivalent yet)
- Removed lmstudio alias from custom profile (it's a separate provider now)
- Skipped openrouter/custom from PROVIDER_REGISTRY auto-extension
  (resolve_provider special-cases them; adding breaks runtime resolution)
- runtime_provider: profile.api_mode only as fallback when URL detection
  finds nothing (was breaking minimax /v1 override)
- Preserved main's legacy-path improvements: deepseek reasoning_content
  preserve, gemini Gemma skip, OpenRouter response caching, Anthropic 1M
  beta recovery, etc.
- Kept agent/copilot_acp_client.py in place (rejected PR's relocation —
  main has 7 fixes landed since; relocation would revert them)
- _API_KEY_PROVIDER_AUX_MODELS alias kept for backward compat with existing
  test imports

Co-authored-by: kshitijk4poor <82637225+kshitijk4poor@users.noreply.github.com>
Closes #14418

website/docs/integrations/providers.md

@@ -480,6 +480,44 @@ model:
 For on-prem deployments (DGX Spark, local GPU), set `NVIDIA_BASE_URL=http://localhost:8000/v1`. NIM exposes the same OpenAI-compatible chat completions API as build.nvidia.com, so switching between cloud and local is a one-line env-var change.
 :::
 
+### GMI Cloud
+
+Open and reasoning models via [GMI Cloud](https://inference.gmi.ai) — OpenAI-compatible API, API key authentication.
+
+```bash
+# GMI Cloud
+hermes chat --provider gmi --model deepseek-ai/DeepSeek-R1
+# Requires: GMI_API_KEY in ~/.hermes/.env
+```
+
+Or set it permanently in `config.yaml`:
+```yaml
+model:
+  provider: "gmi"
+  default: "deepseek-ai/DeepSeek-R1"
+```
+
+The base URL can be overridden with `GMI_BASE_URL` (default: `https://api.gmi.ai/v1`).
+
+### StepFun
+
+Step-series models via [StepFun](https://platform.stepfun.com) — OpenAI-compatible API, API key authentication.
+
+```bash
+# StepFun
+hermes chat --provider stepfun --model step-3-mini
+# Requires: STEPFUN_API_KEY in ~/.hermes/.env
+```
+
+Or set it permanently in `config.yaml`:
+```yaml
+model:
+  provider: "stepfun"
+  default: "step-3-mini"
+```
+
+The base URL can be overridden with `STEPFUN_BASE_URL` (default: `https://api.stepfun.com/v1`).
+
 ### Hugging Face Inference Providers
 
 [Hugging Face Inference Providers](https://huggingface.co/docs/inference-providers) routes to 20+ open models through a unified OpenAI-compatible endpoint (`router.huggingface.co/v1`). Requests are automatically routed to the fastest available backend (Groq, Together, SambaNova, etc.) with automatic failover.
@@ -1239,7 +1277,7 @@ fallback_model:
 
 When activated, the fallback swaps the model and provider mid-session without losing your conversation. It fires **at most once** per session.
 
-Supported providers: `openrouter`, `nous`, `openai-codex`, `copilot`, `copilot-acp`, `anthropic`, `gemini`, `google-gemini-cli`, `qwen-oauth`, `huggingface`, `zai`, `kimi-coding`, `kimi-coding-cn`, `minimax`, `minimax-cn`, `minimax-oauth`, `deepseek`, `nvidia`, `xai`, `ollama-cloud`, `bedrock`, `ai-gateway`, `opencode-zen`, `opencode-go`, `kilocode`, `xiaomi`, `arcee`, `gmi`, `alibaba`, `tencent-tokenhub`, `custom`.
+Supported providers: `openrouter`, `nous`, `openai-codex`, `copilot`, `copilot-acp`, `anthropic`, `gemini`, `google-gemini-cli`, `qwen-oauth`, `huggingface`, `zai`, `kimi-coding`, `kimi-coding-cn`, `minimax`, `minimax-cn`, `minimax-oauth`, `deepseek`, `nvidia`, `xai`, `ollama-cloud`, `bedrock`, `ai-gateway`, `opencode-zen`, `opencode-go`, `kilocode`, `xiaomi`, `arcee`, `gmi`, `stepfun`, `alibaba`, `tencent-tokenhub`, `custom`.
 
 :::tip
 Fallback is configured exclusively through `config.yaml` — there are no environment variables for it. For full details on when it triggers, supported providers, and how it interacts with auxiliary tasks and delegation, see [Fallback Providers](/docs/user-guide/features/fallback-providers).