Add Context7 remote MCP server to auto-generated config

Context7 provides up-to-date library documentation for LLMs via a
remote endpoint — no local binary needed. Always registered since it
has no PATH dependency.

Also switches generated config from .json to .jsonc so we can include
a comment about the optional API key for higher rate limits. The
existing-config check now detects both file extensions.

rootfs/usr/local/lib/opencode-devbox/generate-config.py

@@ -96,6 +96,14 @@ def register_mcp_servers(config: dict) -> list[str]:
             "enabled": False,
         }
 
+    # Context7 — up-to-date library documentation for LLMs (remote).
+    # Free tier works without an API key; set CONTEXT7_API_KEY for higher
+    # rate limits. No local binary needed — purely a remote MCP endpoint.
+    servers["context7"] = {
+        "type": "remote",
+        "url": "https://mcp.context7.com/mcp",
+    }
+
     if servers:
         config["mcp"] = servers
 
@@ -110,14 +118,17 @@ def main() -> int:
 
     home = Path(os.environ.get("HOME", "/home/developer"))
     config_dir = home / ".config" / "opencode"
-    config_file = config_dir / "opencode.json"
+    config_file = config_dir / "opencode.jsonc"
+    config_file_legacy = config_dir / "opencode.json"
 
     # CRITICAL: never overwrite an existing config. Users may have
     # bind-mounted their host config directory, or their config may be
     # persisted in a named volume from a previous run.
-    if config_file.exists():
+    # Check both .json and .jsonc variants.
+    if config_file.exists() or config_file_legacy.exists():
+        existing = config_file if config_file.exists() else config_file_legacy
         print(
-            f"Existing opencode.json found at {config_file} — "
+            f"Existing config found at {existing} — "
             "skipping generation.",
             file=sys.stderr,
         )
@@ -140,8 +151,23 @@ def main() -> int:
     added = register_mcp_servers(config)
 
     config_dir.mkdir(parents=True, exist_ok=True)
+
+    # Write as JSONC so we can include helpful comments.
+    content = json.dumps(config, indent=2)
+
+    # Insert a comment about Context7 API key after the context7 url line.
+    context7_comment = (
+        '      "url": "https://mcp.context7.com/mcp"\n'
+        "      // For higher rate limits, sign up at https://context7.com/dashboard\n"
+        '      // and add: "headers": { "CONTEXT7_API_KEY": "{env:CONTEXT7_API_KEY}" }'
+    )
+    content = content.replace(
+        '      "url": "https://mcp.context7.com/mcp"',
+        context7_comment,
+    )
+
     with config_file.open("w") as f:
-        json.dump(config, f, indent=2)
+        f.write(content)
         f.write("\n")
 
     if added: