feat: Dynamic Model/Provider System with Auto-Install CLIs

[MikeeBuilds]

Summary

Adds a complete dynamic model/provider system inspired by Auto-Claude.

Features

• 6-Terminal Grid: Pre-spawned terminals in a 3x2 grid layout
• Provider Selection: Per-terminal dropdown to switch between Claude, Gemini, Codex, OpenCode, Cursor, or Shell
• Model Selection: Per-terminal model picker (Sonnet 4, Opus, Haiku, etc.)
• Auto-Install: CLIs are automatically installed when first selected (via npx or curl)
• Secure API Keys: Stored using Electron safeStorage (encrypted at rest)
• Settings UI: API key management panel accessible from System Config
• Task Linking: Link terminals to Kanban tasks with context injection

Files Added

• \settings-store.ts\ - Encrypted API key storage
• \SettingsPanel.tsx\ - Settings UI
• \TerminalHub.tsx\ - 6-terminal grid
• \XTermComponent.tsx\ - xterm.js wrapper
• \providers.ts\ - Provider configurations

Testing

• Gemini CLI tested
• OpenAI Codex (needs key)
• Claude Code (needs key)

Closes #7