feat: add opencode module (#515)

## Description

This PR adds the opencode module to the registry.

## Type of Change

- [x] New module
- [ ] New template
- [ ] Bug fix
- [ ] Feature/enhancement
- [ ] Documentation
- [ ] Other

## Module Information

<!-- Delete this section if not applicable -->

**Path:** `registry/coder-labs/modules/opencode`  
**New version:** `v0.1.0`  
**Breaking change:** [ ] Yes [x] No

## Testing & Validation

- [x] Tests pass (`bun test`)
- [x] Code formatted (`bun fmt`)
- [x] Changes tested locally

## Related Issues

<!-- Link related issues or write "None" if not applicable -->

---------

Co-authored-by: DevCats <christofer@coder.com>

Author: 35C4n0r

.icons/opencode.svg

@@ -0,0 +1,108 @@
+---
+display_name: OpenCode
+icon: ../../../../.icons/opencode.svg
+description: Run OpenCode AI coding assistant for AI-powered terminal assistance
+verified: false
+tags: [agent, opencode, ai, tasks]
+---
+
+# OpenCode
+
+Run [OpenCode](https://opencode.ai) AI coding assistant in your workspace for intelligent code generation, analysis, and development assistance. This module integrates with [AgentAPI](https://github.com/coder/agentapi) for seamless task reporting in the Coder UI.
+
+```tf
+module "opencode" {
+  source   = "registry.coder.com/coder-labs/opencode/coder"
+  version  = "0.1.0"
+  agent_id = coder_agent.example.id
+  workdir  = "/home/coder/project"
+}
+```
+
+## Prerequisites
+
+- **Authentication credentials** - OpenCode auth.json file is required for non-interactive authentication, you can find this file on your system: `$HOME/.local/share/opencode/auth.json`
+
+## Examples
+
+### Basic Usage with Tasks
+
+```tf
+resource "coder_ai_task" "task" {
+  app_id = module.opencode.task_app_id
+}
+
+module "opencode" {
+  source   = "registry.coder.com/coder-labs/opencode/coder"
+  version  = "0.1.0"
+  agent_id = coder_agent.example.id
+  workdir  = "/home/coder/project"
+
+  ai_prompt = coder_ai_task.task.prompt
+
+  auth_json = <<-EOT
+{
+  "google": {
+    "type": "api",
+    "key": "gem-xxx-xxxx"
+  },
+  "anthropic": {
+    "type": "api",
+    "key": "sk-ant-api03-xxx-xxxxxxx"
+  }
+}
+EOT
+
+  config_json = jsonencode({
+    "$schema" = "https://opencode.ai/config.json"
+    mcp = {
+      filesystem = {
+        command = ["npx", "-y", "@modelcontextprotocol/server-filesystem", "/home/coder/projects"]
+        enabled = true
+        type    = "local"
+        environment = {
+          SOME_VARIABLE_X = "value"
+        }
+      }
+      playwright = {
+        command = ["npx", "-y", "@playwright/mcp@latest", "--headless", "--isolated"]
+        enabled = true
+        type    = "local"
+      }
+    }
+    model = "anthropic/claude-sonnet-4-20250514"
+  })
+
+  pre_install_script = <<-EOT
+    #!/bin/bash
+    curl -fsSL https://deb.nodesource.com/setup_22.x | sudo -E bash -
+    sudo apt-get install -y nodejs
+  EOT
+}
+```
+
+### Standalone CLI Mode
+
+Run OpenCode as a command-line tool without web interface or task reporting:
+
+```tf
+module "opencode" {
+  source       = "registry.coder.com/coder-labs/opencode/coder"
+  version      = "0.1.0"
+  agent_id     = coder_agent.example.id
+  workdir      = "/home/coder"
+  report_tasks = false
+  cli_app      = true
+}
+```
+
+## Troubleshooting
+
+If you encounter any issues, check the log files in the `~/.opencode-module` directory within your workspace for detailed information.
+
+## References
+
+- [Opencode JSON Config](https://opencode.ai/docs/config/)
+- [OpenCode Documentation](https://opencode.ai/docs)
+- [AgentAPI Documentation](https://github.com/coder/agentapi)
+- [Coder AI Agents Guide](https://coder.com/docs/tutorials/ai-agents)