[FEATURE] Display usage counts in /skills command

Problem

The /skills command currently shows only token counts for each skill. With dozens (or in some orgs, hundreds) of skills installed, token count alone isn't enough signal to decide what's worth keeping, pinning, or removing. The more useful signal — "how often do I actually use this skill?" — is already being tracked locally, just not surfaced.

~/.claude.json already stores per-skill usage data:

"yeet:issue": {
  "usageCount": 69,
  "lastUsedAt": 1776415180600
}

So the data is right there — it just isn't shown anywhere in the UI.

Proposed solution

In the /skills picker, add a column (or inline suffix) next to each skill showing:

• usageCount — total invocations
• optionally lastUsedAt as a relative timestamp (e.g. 2d ago)

Sort order could optionally default to most-used first, or stay alphabetical with the count shown on the right.

Rough mock:

/skills

  yeet:issue            ~1.2k tokens   69 uses   2d ago
  commit                ~800 tokens    41 uses   5h ago
  find-skills           ~600 tokens     3 uses   30d ago
  …

No new tracking needed — just read what's already in claude.json.

Alternatives considered

• Writing a separate shell script that parses claude.json and prints usage stats. Works, but duplicates data the TUI already has access to, and doesn't help in the moment I'm picking a skill.
• Waiting for full skill analytics (#35319). That issue proposes a much bigger system (local JSONL log, CLI stats command, OTEL/webhook export). This request is a tiny subset — just display the counter that's already being incremented.

Priority

Low

Category

Interactive mode (TUI)