feat: Add OpenCode provider integration with official brand icons

This commit integrates OpenCode as a new AI provider and updates all provider
icons with their official brand colors for better visual recognition.

**OpenCode Provider Integration:**
- Add OpencodeProvider class with CLI-based execution
- Support for OpenCode native models (opencode/) and Bedrock models
- Proper event normalization for OpenCode streaming format
- Correct CLI arguments: --format json (not stream-json)
- Event structure: type, part.text, sessionID fields

**Provider Icons:**
- Add official OpenCode icon (white square frame from opencode.ai)
- Add DeepSeek icon (blue whale #4D6BFE)
- Add Qwen icon (purple gradient #6336E7 → #6F69F7)
- Add Amazon Nova icon (AWS orange #FF9900)
- Add Mistral icon (rainbow gradient gold→red)
- Add Meta icon (blue #1877F2)
- Update existing icons with brand colors:
  * Claude: #d97757 (terra cotta)
  * OpenAI/Codex: #74aa9c (teal-green)
  * Cursor: #5E9EFF (bright blue)

**Settings UI Updates:**
- Update settings navigation to show OpenCode icon
- Update model configuration to use provider-specific icons
- Differentiate between OpenCode free models and Bedrock-hosted models
- All AI models now display their official brand logos

**Model Resolution:**
- Add isOpencodeModel() function to detect OpenCode models
- Support patterns: opencode/, opencode-*, amazon-bedrock/*
- Update getProviderFromModel to recognize opencode provider

Note: Some unit tests in opencode-provider.test.ts need updating to match
the new event structure and CLI argument format.

apps/ui/src/components/views/settings-view/config/navigation.ts

@@ -14,9 +14,8 @@ import {
   MessageSquareText,
   User,
   Shield,
-  Cpu,
 } from 'lucide-react';
-import { AnthropicIcon, CursorIcon, OpenAIIcon } from '@/components/ui/provider-icon';
+import { AnthropicIcon, CursorIcon, OpenAIIcon, OpenCodeIcon } from '@/components/ui/provider-icon';
 import type { SettingsViewId } from '../hooks/use-settings-view';
 
 export interface NavigationItem {
@@ -48,7 +47,7 @@ export const GLOBAL_NAV_GROUPS: NavigationGroup[] = [
           { id: 'claude-provider', label: 'Claude', icon: AnthropicIcon },
           { id: 'cursor-provider', label: 'Cursor', icon: CursorIcon },
           { id: 'codex-provider', label: 'Codex', icon: OpenAIIcon },
-          { id: 'opencode-provider', label: 'OpenCode', icon: Cpu },
+          { id: 'opencode-provider', label: 'OpenCode', icon: OpenCodeIcon },
         ],
       },
       { id: 'mcp-servers', label: 'MCP Servers', icon: Plug },