aitools list: emit JSON via --output json

[jamesbroadhead]

Summary

databricks aitools list learns --output json, emitting a structured document so coding agents and CI can consume the skill/version/installation matrix without scraping the tabwriter text output. Text rendering is unchanged.

Stacked on #4917 (uses --scope and the moved-to-top-level aitools/ package). Base will rebase to main once #4917 merges.

JSON shape

{
  "release": "0.1.0",
  "skills": [
    {
      "name": "databricks-jobs",
      "latest_version": "1.0.0",
      "experimental": false,
      "installed": { "global": "1.0.0", "project": "0.9.0" }
    }
  ],
  "summary": {
    "global":  { "installed": 5, "total": 10 },
    "project": { "installed": 3, "total": 10 }
  }
}

• installed is keyed by scope; absent key = not installed in that scope; empty map = not installed anywhere.
• summary only includes scopes that were queried, so --scope=global narrows it to one key.
• release is the version string without the v prefix.

This is the documented public contract — field names and types should not change without a major version bump.

Why

aitools list is one of the surfaces an agent reaches for first ("what's installed, what's available, what's stale"). Scraping tabwriter columns from stderr is fragile; a stable JSON contract makes the command declarative for non-human callers. Matches the convention used by other CLI commands that already honor --output json (bundle validate, pipelines run, etc.).

Test plan

• databricks aitools list --output json against a workspace with a mix of installed/uninstalled skills, both scopes — JSON validates against the shape above.
• databricks aitools list --output json --scope=global — summary only contains global.
• databricks aitools list (no --output) — output is byte-for-byte unchanged from main.
• Unit: TestRenderListJSON, TestRenderListJSONScopeFiltersSummary, TestInstalledStatusFromEntry cover the rendering paths.

This pull request was AI-assisted by Isaac.

[jamesbroadhead]

👋 @simonfaltum — Claude here on James's behalf.

Rebased onto the new tip of #5234 (which itself was rebased onto current main after #4917 landed) and flipped this out of draft. The diff is now small (3 files, +283/-71) showing only the actual --output json work.

Drift fixes applied during the rebase:

• ListSkillsFn → listSkillsFn (matches Promote aitools skills-management commands to top-level #4917's final review feedback that made these unexported)
• installer.GetSkillsRef updated to the 3-value (ref, explicit, err) signature now in main
• Import paths rewritten from aitools/lib/... to libs/aitools/...

Stacking note: PR base is set to jb/aitools-interface (#5234), not main. Once #5234 merges, GitHub will auto-retarget the base.

Ready for review whenever you've got time.

(comment posted by Claude)

[simonfaltum]

Looks good after the fixes on this branch.

I also merged the latest stacked base/main, resolved the changelog/list conflicts, restored manifest fallback behavior, and added coverage for preserving scoped text labels while adding JSON output.