Add dedicated error display panel to TUI for DevHub core errors

[diyor28]

Add Dedicated Error Display Panel to TUI

Problem

Currently, DevHub TUI has limited error visibility:

• Service errors are only shown inline with service status (ErrorMsg field)
• Core DevHub errors (MCP server, state manager, etc.) are silently ignored or logged to stderr
• No centralized error view for debugging issues
• Users have no way to see system-level errors within the TUI

Proposed Solution

Add a dedicated error panel to the TUI that displays:

1. Service-level errors - Current ErrorMsg from services
2. Core system errors - MCP server, StateManager, ServiceManager errors
3. Application errors - Configuration, dependency resolution, etc.
4. Historical error log - Recent errors with timestamps

Relevant Files

• devhub.go - Main application entry point where core errors are silently ignored
• view.go - TUI rendering logic that needs error panel
• types.go - Data structures for UI state
• update.go - Key handling for error panel navigation
• mcp_server.go - MCP server errors that need capturing
• state_manager.go - State management errors
• service_manager.go - Service management errors

Proposed ASCII Layout

╭──────────────────────────────────────────────────────────────────────────────╮
│                          🚀 DevHub - Error Panel                            │
│                       Development Tools Manager                              │
├──────────────────────────────────────────────────────────────────────────────┤
│ 📦 5 services  •  ✅ 3 running  •  ❌ 2 errors                              │
├──────────────────────────────────────────────────────────────────────────────┤
│ Services:  ⚡ 45.2%  💾 512.3 MB                                            │
│ System:    ⚡ 23.1%  💾 8.2 GB (68%)                                        │
╰──────────────────────────────────────────────────────────────────────────────╯

┌─ Errors (E to toggle) ─────────────────────────────────────────────────────┐
│ 🔴 [18:01:45] MCP Server: Failed to bind to port 8765 (address in use)    │
│ ⚠️  [18:01:23] postgres: Health check timeout after 30s                   │
│ 🔴 [18:00:12] redis: Process terminated unexpectedly (exit code 1)        │
│ ⚠️  [17:59:45] StateManager: Resource monitoring failed for service 'api'  │
└────────────────────────────────────────────────────────────────────────────┘

▶ postgres (Failed)                                    🔴 Error
  PostgreSQL Database Server
  PID: 1234 | Uptime: 5m23s | CPU: 2.1% | Mem: 45.2MB
  Dependencies: none

  redis (Running)                                      ◉ Running  
  Redis Cache Server
  PID: 5678 | Uptime: 10m12s | CPU: 1.5% | Mem: 23.1MB

↑/↓: Navigate • Space: Toggle • r: Restart • Enter: View Logs • E: Errors • q: Quit

Implementation Details

1. Error Collection System

type ErrorEntry struct {
    Timestamp time.Time
    Source    string // "service:postgres", "mcp", "state", etc.
    Level     ErrorLevel // Error, Warning, Info
    Message   string
}

type ErrorManager struct {
    errors []ErrorEntry
    mu     sync.RWMutex
    maxEntries int
}

2. UI State Updates

// In types.go
type UIState struct {
    Width         int
    Height        int
    SelectedIndex int
    ViewMode      ViewMode
    ShowErrors    bool  // New: toggle error panel
    ErrorScroll   int   // New: scroll position in error panel
    // ... existing fields
}

// New view mode
const (
    ServiceView ViewMode = iota
    LogView
    ErrorView  // New: dedicated error view
)

3. Key Bindings

• E: Toggle error panel visibility
• Shift+E: Switch to full error view
• In error view: ↑/↓ scroll, Enter for details, C to clear

4. Error Sources to Capture

• MCP Server errors: Port binding, request handling
• Service Manager errors: Start/stop failures, dependency issues
• State Manager errors: Resource monitoring, update failures
• Configuration errors: Invalid YAML, missing dependencies
• Health Check errors: Timeout, connection failures

Acceptance Criteria

• Error panel toggles with E key
• Shows recent errors with timestamps and sources
• Color-coded by severity (red=error, yellow=warning, blue=info)
• Scrollable when more errors than display space
• Integrates with existing service error display
• Error panel auto-shows when new errors occur
• Errors are categorized by source (service, core, system)
• Historical error persistence during session
• Clear errors functionality