aitools: add --scope flag, deprecate --project/--global

[jamesbroadhead]

Summary

Split out from #4917. While that PR keeps responsibility for moving the aitools skills-management surface out of experimental/, this PR makes the user-facing interface changes that should land at the same moment:

• New --scope=project|global flag on install/update/uninstall/list, with --scope=both accepted by update and list.
• --project and --global are marked deprecated via cobra's Deprecated property: hidden from --help, emit a stderr deprecation warning when used, continue to function so existing scripts don't break. They're slated for removal in a later release.
• --scope combined with --project/--global is rejected up front with an actionable error.
• install's --help now documents the non-interactive --agents auto-detect contract so callers know what gets picked.

Stacked on #4917. Base will rebase to main once that lands. Splitting because (a) #4917 is otherwise a pure file move and reviewers asked to keep it that way, and (b) the interface change has its own product question (boolean pair vs. enum) worth landing as a discrete unit.

Why land this with the rename

aitools is being declared a stable top-level surface in #4917. This is the cheapest moment to fix the two-boolean shape before external scripts depend on it. An enum is also better for agent-driven invocations than two booleans with implicit precedence: --scope=project|global|both is one flag with valid values, not two flags with order-dependent semantics.

Surface

databricks aitools install   --scope=project|global             (--scope=both rejected)
databricks aitools uninstall --scope=project|global             (--scope=both rejected)
databricks aitools update    --scope=project|global|both
databricks aitools list      --scope=project|global|both        (default: both)

databricks aitools install --project    # warns: use --scope=project
databricks aitools install --global     # warns: use --scope=global

Test plan

• databricks aitools install --scope=project and --scope=global go to the right destination
• databricks aitools install --scope=both errors with a clear message
• databricks aitools install --project still works and prints the deprecation warning to stderr
• databricks aitools install --scope=global --project errors with the conflict message
• databricks aitools list --scope=both shows both scopes (equivalent to no flag)
• databricks aitools install --help no longer shows --project/--global; --scope is documented; --agents auto-detect behavior is described
• Unit: TestParseScopeFlag (table-driven on the translation), TestInstallScopeFlag, TestListScopeFlag — all green

This pull request was AI-assisted by Isaac.

[github-actions]

Approval status: pending

/aitools/ - needs approval

8 files changed
Eligible: @fjakobs, @Shridhad, @atilafassina, @keugenek, @arsenyinfo, @igrekun, @pkosiec, @MarioCadenas, @pffigueiredo, @ditadi, @calvarjorge, @lennartkats-db

General files (require maintainer)

Files: NEXT_CHANGELOG.md
Based on git history:

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

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