Promote aitools from experimental to top-level command

[jamesbroadhead]

Summary

• Promotes the aitools skills-management surface to top-level databricks aitools: install, update, uninstall, list, version, and the (hidden) skills alias group
• Removes Hidden: true from those commands so they show up under databricks --help
• Preserves databricks experimental aitools <skill-cmd> as a hidden, deprecated alias that prints a warning pointing users at the new path
• Keeps databricks experimental aitools tools (query, discover-schema, get-default-warehouse, statement) under experimental for now — that subtree's own help text says "There are no stability guarantees for these tools," so it shouldn't graduate yet
• The deprecation warning fires for skills subcommands (which have a top-level replacement) but not for tools subcommands (which don't)

The aitools skills-management surface is feature-complete after the 5-PR series (#4810–#4814) that added state tracking, lifecycle commands (install/update/uninstall/list/version), and project scope support. The tools subtree is functionally useful but its shape is still in flux, so promoting only the stable half.

Command shape after this PR

# Stable, top-level
databricks aitools install [skill-name]
databricks aitools update
databricks aitools uninstall
databricks aitools list
databricks aitools version
databricks aitools skills {list,install}        # hidden alias group

# Experimental, unchanged path
databricks experimental aitools tools query
databricks experimental aitools tools discover-schema
databricks experimental aitools tools get-default-warehouse
databricks experimental aitools tools statement {submit,get,status,cancel}

# Deprecated alias — warns and forwards
databricks experimental aitools install/update/uninstall/list/version/skills

Implementation note for reviewers: cobra picks the nearest ancestor's PersistentPreRunE, so attaching tools under the experimental alias with its own non-warning hook overrides the alias's deprecation warning for tools-rooted invocations. Both hooks chain to the root's PersistentPreRunE so IO/log/user-agent setup is preserved.

Test plan

• databricks aitools --help shows install/update/uninstall/list/version (no tools)
• databricks --help lists aitools in the output
• databricks experimental aitools install prints deprecation warning, runs, and the work happens
• databricks experimental aitools tools query … does NOT print the warning
• databricks experimental aitools tools --help lists query/discover-schema/get-default-warehouse/statement
• Existing aitools tests pass

This pull request was AI-assisted by Isaac.

[github-actions]

Approval status: pending

/cmd/apps/ - needs approval

Files: cmd/apps/init.go
Suggested: @pkosiec
Also eligible: @MarioCadenas, @arsenyinfo, @fjakobs, @keugenek, @calvarjorge, @Shridhad, @atilafassina, @igrekun, @pffigueiredo, @ditadi

/experimental/aitools/ - needs approval

Files: experimental/aitools/README.md, experimental/aitools/cmd/aitools.go
Suggested: @pkosiec
Also eligible: @MarioCadenas, @arsenyinfo, @fjakobs, @lennartkats-db, @keugenek, @calvarjorge, @Shridhad, @atilafassina, @igrekun, @pffigueiredo, @ditadi

General files (require maintainer)

59 files changed
Based on git history:

• @simonfaltum -- recent work in ./, .github/, experimental/aitools/cmd/

_{Any maintainer (@andrewnester, @anton-107, @denik, @pietern, @shreyas-goenka, @simonfaltum, @renaudhartert-db) can approve all areas.
See OWNERS for ownership rules.}

[simonfaltum]

I think we should move the code itself (the files) out of experimental as part of this as well.