Feature request: Add subagent-style progress rendering for skill execution

Summary

Skills currently execute with no visible progress UI — they're transparent to the user. In contrast, subagents show a rich progress experience with animated spinners, task name/status, token tracking, and completion notifications. Skill execution should get similar treatment.

Current Behavior

When a skill (e.g., /optimize, /fix, /inspect) is invoked:

• No spinner or progress indicator is shown
• No token count or effort level display
• No status updates during execution
• The user sees no feedback until the skill produces output

Desired Behavior

Skill execution should show progress similar to subagents:

• Animated spinner with the skill name (e.g., "Running /optimize...")
• Token tracking showing context usage during skill execution
• Status updates as the skill progresses through stages
• Completion notification when the skill finishes
• Colored indicators matching the existing subagent color scheme

Context

The subagent progress rendering has been significantly improved over recent releases (per CHANGELOG):

• Spinner with effort level display
• activeForm field for custom status text (with fallback to task subject)
• Memory-optimized progress payloads during context compaction
• Custom spinner colors per agent

Skills would benefit from reusing these same components rather than remaining invisible during execution.

Use Case

As a user running complex skills like /fix (which orchestrates multiple sub-operations) or /optimize (which loads references, analyzes code, and generates reports), I want to see real-time progress so I know the skill is working and roughly how far along it is.