feat(provider): add OpenCode Zen and OpenCode Go providers

Add support for OpenCode Zen (pay-as-you-go, 35+ curated models) and
OpenCode Go ($10/month subscription, open models) as first-class providers.

Both are OpenAI-compatible endpoints resolved via the generic api_key
provider flow — no custom adapter needed.

Files changed:
- hermes_cli/auth.py — ProviderConfig entries + aliases
- hermes_cli/config.py — OPENCODE_ZEN/GO API key env vars
- hermes_cli/models.py — model catalogs, labels, aliases, provider order
- hermes_cli/main.py — provider labels, menu entries, model flow dispatch
- hermes_cli/setup.py — setup wizard branches (idx 10, 11)
- agent/model_metadata.py — context lengths for all OpenCode models
- agent/auxiliary_client.py — default aux models
- .env.example — documentation

Co-authored-by: DevAgarwal2 <DevAgarwal2@users.noreply.github.com>

hermes_cli/config.py

@@ -485,6 +485,38 @@ OPTIONAL_ENV_VARS = {
         "password": False,
         "category": "provider",
     },
+    "OPENCODE_ZEN_API_KEY": {
+        "description": "OpenCode Zen API key (pay-as-you-go access to curated models)",
+        "prompt": "OpenCode Zen API key",
+        "url": "https://opencode.ai/auth",
+        "password": True,
+        "category": "provider",
+        "advanced": True,
+    },
+    "OPENCODE_ZEN_BASE_URL": {
+        "description": "OpenCode Zen base URL override",
+        "prompt": "OpenCode Zen base URL (leave empty for default)",
+        "url": None,
+        "password": False,
+        "category": "provider",
+        "advanced": True,
+    },
+    "OPENCODE_GO_API_KEY": {
+        "description": "OpenCode Go API key ($10/month subscription for open models)",
+        "prompt": "OpenCode Go API key",
+        "url": "https://opencode.ai/auth",
+        "password": True,
+        "category": "provider",
+        "advanced": True,
+    },
+    "OPENCODE_GO_BASE_URL": {
+        "description": "OpenCode Go base URL override",
+        "prompt": "OpenCode Go base URL (leave empty for default)",
+        "url": None,
+        "password": False,
+        "category": "provider",
+        "advanced": True,
+    },
 
     # ── Tool API keys ──
     "FIRECRAWL_API_KEY": {