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

providers/copilot.py

@@ -0,0 +1,58 @@
+"""Copilot / GitHub Models provider profile.
+
+Copilot uses per-model api_mode routing:
+  - GPT-5+ / Codex models → codex_responses
+  - Claude models → anthropic_messages
+  - Everything else → chat_completions (this profile covers that subset)
+
+Key quirks for the chat_completions subset:
+  - Editor attribution headers (via copilot_default_headers())
+  - GitHub Models reasoning extra_body (model-catalog gated)
+"""
+
+from typing import Any
+
+from providers import register_provider
+from providers.base import ProviderProfile
+
+
+class CopilotProfile(ProviderProfile):
+    """GitHub Copilot / GitHub Models — editor headers + reasoning."""
+
+    def build_api_kwargs_extras(
+        self,
+        *,
+        model: str | None = None,
+        reasoning_config: dict | None = None,
+        supports_reasoning: bool = False,
+        **ctx,
+    ) -> tuple[dict[str, Any], dict[str, Any]]:
+        extra_body: dict[str, Any] = {}
+        if supports_reasoning and model:
+            try:
+                from hermes_cli.models import github_model_reasoning_efforts
+
+                supported_efforts = github_model_reasoning_efforts(model)
+                if supported_efforts and reasoning_config:
+                    effort = reasoning_config.get("effort", "medium")
+                    # Normalize non-standard effort levels to the nearest supported
+                    if effort == "xhigh":
+                        effort = "high"
+                    if effort in supported_efforts:
+                        extra_body["reasoning"] = {"effort": effort}
+                elif supported_efforts:
+                    extra_body["reasoning"] = {"effort": "medium"}
+            except Exception:
+                pass
+        return extra_body, {}
+
+
+copilot = CopilotProfile(
+    name="copilot",
+    aliases=("github-copilot", "github-models", "github-model", "github"),
+    env_vars=("COPILOT_GITHUB_TOKEN", "GH_TOKEN", "GITHUB_TOKEN"),
+    base_url="https://api.githubcopilot.com",
+    auth_type="copilot",
+)
+
+register_provider(copilot)