feat(qwen): add Qwen OAuth provider with portal request support

Based on #6079 by @tunamitom with critical fixes and comprehensive tests.

Changes from #6079:
- Fix: sanitization overwrite bug — Qwen message prep now runs AFTER codex
  field sanitization, not before (was silently discarding Qwen transforms)
- Fix: missing try/except AuthError in runtime_provider.py — stale Qwen
  credentials now fall through to next provider on auto-detect
- Fix: 'qwen' alias conflict — bare 'qwen' stays mapped to 'alibaba'
  (DashScope); use 'qwen-portal' or 'qwen-cli' for the OAuth provider
- Fix: hardcoded ['coder-model'] replaced with live API fetch + curated
  fallback list (qwen3-coder-plus, qwen3-coder)
- Fix: extract _is_qwen_portal() helper + _qwen_portal_headers() to replace
  5 inline 'portal.qwen.ai' string checks and share headers between init
  and credential swap
- Fix: add Qwen branch to _apply_client_headers_for_base_url for mid-session
  credential swaps
- Fix: remove suspicious TypeError catch blocks around _prompt_provider_choice
- Fix: handle bare string items in content lists (were silently dropped)
- Fix: remove redundant dict() copies after deepcopy in message prep
- Revert: unrelated ai-gateway test mock removal and model_switch.py comment deletion

New tests (30 test functions):
- _qwen_cli_auth_path, _read_qwen_cli_tokens (success + 3 error paths)
- _save_qwen_cli_tokens (roundtrip, parent creation, permissions)
- _qwen_access_token_is_expiring (5 edge cases: fresh, expired, within skew,
  None, non-numeric)
- _refresh_qwen_cli_tokens (success, preserve old refresh, 4 error paths,
  default expires_in, disk persistence)
- resolve_qwen_runtime_credentials (fresh, auto-refresh, force-refresh,
  missing token, env override)
- get_qwen_auth_status (logged in, not logged in)
- Runtime provider resolution (direct, pool entry, alias)
- _build_api_kwargs (metadata, vl_high_resolution_images, message formatting,
  max_tokens suppression)

hermes_cli/models.py

@@ -483,6 +483,7 @@ _PROVIDER_LABELS = {
     "ai-gateway": "AI Gateway",
     "kilocode": "Kilo Code",
     "alibaba": "Alibaba Cloud (DashScope)",
+    "qwen-oauth": "Qwen OAuth (Portal)",
     "huggingface": "Hugging Face",
     "custom": "Custom endpoint",
 }
@@ -522,6 +523,7 @@ _PROVIDER_ALIASES = {
     "aliyun": "alibaba",
     "qwen": "alibaba",
     "alibaba-cloud": "alibaba",
+    "qwen-portal": "qwen-oauth",
     "hf": "huggingface",
     "hugging-face": "huggingface",
     "huggingface-hub": "huggingface",
@@ -767,6 +769,7 @@ def list_available_providers() -> list[dict[str, str]]:
         "openrouter", "nous", "openai-codex", "copilot", "copilot-acp",
         "gemini", "huggingface",
         "zai", "kimi-coding", "minimax", "minimax-cn", "kilocode", "anthropic", "alibaba",
+        "qwen-oauth",
         "opencode-zen", "opencode-go",
         "ai-gateway", "deepseek", "custom",
     ]