feat(app): add opencode sidecar support as AI provider

[louis030195]

Summary

Adds OpenCode as a dedicated feature in the screenpipe app. OpenCode is an agentic coding AI that can be spawned as a sidecar process.

Important: OpenCode is NOT an OpenAI-compatible API, so it cannot be a simple AI preset. Instead, this PR creates a dedicated OpenCode chat interface at /opencode.

Architecture

┌─────────────────┐     invoke()      ┌──────────────────┐
│  OpenCodeChat   │ ──────────────────▶│  Tauri Rust      │
│  (React)        │                    │  (opencode_*)    │
└────────┬────────┘                    └────────┬─────────┘
         │                                      │
         │  @opencode-ai/sdk                    │ spawn sidecar
         │  (HTTP + Basic Auth)                 ▼
         │                            ┌──────────────────┐
         └────────────────────────────▶│  opencode serve  │
                                       │  :random_port    │
                                       └──────────────────┘

Changes

Rust Backend (src-tauri/src/opencode.rs)

• opencode_start(projectDir) - Spawns OpenCode on a random port with:
  • UUID-based HTTP Basic Auth credentials
  • Health check polling (waits for server to be ready)
  • Proper error messages with install instructions
• opencode_stop() - Kills the sidecar (supports macOS, Linux, Windows)
• opencode_info() - Returns current sidecar state
• opencode_check() - Checks if OpenCode is available
• cleanup_opencode() - Called on app exit to clean up

Frontend

• /opencode route - Dedicated OpenCode chat page
• OpenCodeChat component - Full chat UI with:
  • Project directory selection
  • Session management (create, list, select)
  • Message display with markdown rendering
  • Install instructions if OpenCode not available
• useOpencode hook - React hook for sidecar management with event listeners

Dependencies

• Added @opencode-ai/sdk for proper API integration

What's NOT included

• OpenCode is NOT added to AI presets (incompatible API)
• No changes to existing chat functionality

Test plan

• Navigate to /opencode
• Verify install instructions shown if OpenCode not installed
• Install OpenCode and refresh
• Select a project directory
• Start OpenCode
• Verify server starts (status shown in header)
• Create a new session
• Send a message
• Verify AI response appears
• Stop OpenCode
• Close app and verify no orphaned processes

🤖 Generated with Claude Code