[FEATURE]: Add unified task state color convention with icons for visual notifications #24404

Problem

OpenCode currently lacks a unified color convention for task states. Users working with multiple projects simultaneously cannot identify at a glance:

1. Which project is currently executing (no visual indicator)
2. What state a task is in (no clear color convention)
3. When a task completes (notification doesn't identify the project)
4. When attention is required (error states blend with normal text)

Proposed Solution

Implement a unified status color convention based on ISO 3864 safety colors and WCAG accessibility standards:

Color + Icon Convention

Accessibility (WCAG 1.4.1)

Each state always includes:

• Color (for those who can perceive it)
• Icon (for color-blind users)
• Text label (for screen readers)

Multi-Project Notifications

When multiple projects are open, notifications must include the project name to distinguish which project triggered the notification.

Related Issues

This feature addresses:

• [FEATURE]: Visual TUI background color change when agent completes a task #20921 - Visual TUI background color change when agent completes
• [FEATURE]: Show a green indicator on project icons when a session is active #23549 - Show green indicator on project icons when session is active
• [FEATURE]: Display subagent status in TUI prompt footer #23784 - Display subagent status in TUI prompt footer
• [FEATURE]: Desktop popup notifications #23842 - Desktop popup notifications
• [FEATURE]: dismissible toasts — user keyboard/click dismiss + plugin programmatic dismiss #23879 - Dismissible toasts
• [FEATURE]: Improve subagent runtime visibility in chat UI #22233 - Improve subagent runtime visibility
• [FEATURE]: Improve busy indicator visibility across projects #15509 - Improve busy indicator visibility across projects