search --json prints update notice after JSON on stdout in non-current versions, breaking machine consumers

[bishopmatthew]

Summary

In skillshare 0.18.9, skillshare search ... --json can append the
update notice to stdout after the JSON payload:

! Update available: 0.18.9 -> 0.19.0
  Run 'skillshare upgrade' to update

That makes stdout invalid JSON and breaks any tool that shells out to
skillshare search --json and unmarshals the result directly.

Affected Version

Observed on 0.18.9.

The failing output itself included:

! Update available: 0.18.9 -> 0.19.0
  Run 'skillshare upgrade' to update

After upgrading to the latest version, the problem no longer reproduces.

Reproduction

Run:

skillshare search bubbletea --json

On 0.18.9, stdout contained:

1. a valid JSON array of results
2. then the update notice appended after the array

So the full stdout was not valid JSON.

Expected

When --json is passed, stdout should contain only JSON.

Any upgrade/update notice should go to stderr, or be suppressed entirely in
JSON mode.

Actual

Stdout was:

[
  {
    "Name": "bubbletea",
    "Description": "Browse Bubbletea TUI framework documentation and examples. Use when working with Bubbletea components, models, commands, or building terminal user interfaces in Go.",
    "Source": "hmans/beans/.claude/skills/bubbletea",
    "Skill": "",
    "Stars": 678,
    "Owner": "hmans",
    "Repo": "beans",
    "Path": ".claude/skills/bubbletea",
    "Tags": null
  }
]

followed by:

! Update available: 0.18.9 -> 0.19.0
  Run 'skillshare upgrade' to update

That causes JSON parsers to fail with errors like:

invalid character '!' after top-level value

Why This Matters

This broke a wrapper tool that shells out to skillshare search --json
and unmarshals stdout directly.

In general, --json is a machine contract, so any human-oriented trailing
text on stdout is a compatibility break.

Suggested Fix

• guarantee that --json writes only JSON to stdout
• move update notices to stderr
• add a regression test for search --json to assert stdout is pure JSON