…mpotent install (#4811)

## PR Stack

1. [1/5] State + release discovery + directory rename (#4810)
2. **[2/5] Install writes state + interactive agent selection** (this
PR)
3. [3/5] Update + uninstall + version commands (#4812)
4. [4/5] List improvements + command restructuring + flags (#4813)
5. [5/5] Project scope (--project/--global) (pending)

**Base**: `simonfaltum/aitools-pr1-state` (PR 1)

## Why

Install currently has no state tracking, no filtering, and outputs every
file download to the console. Users can't tell what version they have,
and there's no way to install for specific agents.

## Changes

Before: `skills install` downloads everything, prints every file, has no
state, no filtering, no agent selection.

Now:
- `InstallSkillsForAgents(ctx, src, agents, opts)` as the core install
function. `InstallAllSkills` becomes a thin wrapper (signature preserved
for `cmd/apps/init.go` compat).
- State written to `.state.json` after successful install. Merges with
existing state (doesn't overwrite).
- Idempotent: second install skips already-present skills with matching
versions.
- Experimental filtering: skip `experimental: true` skills by default.
- `min_cli_version` enforcement: skip incompatible skills with warning
(hard error for single-skill install).
- Interactive agent selection via `charmbracelet/huh` multi-select. Skip
prompt for 1 agent, all detected for non-interactive.
- Legacy install detection: prints "reinstall" message when old install
found without state.
- Concise default output (2 lines). Per-file detail only at debug level.

## Test plan

- [x] State created after install-all and install-single
- [x] Experimental filtering (skip by default, include with flag)
- [x] min_cli_version: warning for all, hard error for single
- [x] Idempotent: skip same version, update changed
- [x] Legacy detection with helpful message
- [x] Interactive prompt for 2+ agents, skip for 1
- [x] Non-interactive: all detected, no prompt
- [x] `InstallAllSkills` signature preserved
- [x] Concise output, per-file at debug level

## PR Stack

1. [1/5] State + release discovery + directory rename (#4810)
2. [2/5] Install writes state + interactive agent selection (#4811)
3. **[3/5] Update + uninstall + version commands** (this PR)
4. [4/5] List improvements + command restructuring + flags (#4813)
5. [5/5] Project scope (--project/--global) (pending)

**Base**: `simonfaltum/aitools-pr2-install` (PR 2)

## Why

Users can install skills but can't update, uninstall, or check what
version they have. These are core lifecycle gaps.

## Changes

Three new commands, each small but grouped because they share patterns.

**`aitools update`**: Compares installed release against latest.
Downloads changed skills. Flags: `--check` (dry run), `--force`
(re-download), `--no-new` (don't auto-add new manifest skills).
Authoritative release detection (distinguishes real API response from
fallback). Applies experimental and min_cli_version filtering. Warns on
skills removed from manifest.

**`aitools uninstall`**: Removes skill directories from canonical
location. Removes symlinks from ALL agent directories (full registry
scan, not just detected). Cleans orphaned symlinks. Only removes
symlinks pointing to canonical dir (safe for third-party skills).
Deletes `.state.json` on success.

**`aitools version`**: Shows installed version, skill count, last
updated date. Best-effort staleness check against latest release.
Graceful offline degradation. Suppresses staleness check when
`DATABRICKS_SKILLS_REF` is set.

## Test plan

- [x] Update: no state -> error, already up to date, version diff, check
dry run, force, no-new, new skill auto-installed, removed skill warning
- [x] Uninstall: removes dirs + symlinks, orphan cleanup, state
deletion, no state -> error, missing dirs handled
- [x] Version: installed/up-to-date, update available, not installed,
offline graceful
- [x] All lint checks pass

…ude-experimental flags (#4813)

## PR Stack

1. [1/5] State + release discovery + directory rename (#4810)
2. [2/5] Install writes state + interactive agent selection (#4811)
3. [3/5] Update + uninstall + version commands (#4812)
4. **[4/5] List improvements + command restructuring + flags** (this PR)
5. [5/5] Project scope (--project/--global) (#4814)

Manifest v2 PR: databricks/databricks-agent-skills#35

**Base**: `simonfaltum/aitools-pr3-lifecycle` (PR 3)

## Why

Commands are nested under `skills` which burns namespace for future
component types (hooks, etc.). There's no way to install specific
skills, target specific agents from the CLI, or see installed status in
the list output.

## Changes

**New `list` command**: Table output with skill names, versions,
installed status, `[experimental]` tags. Sorted alphabetically. Uses
`tabwriter` for alignment.

**Flat command structure**: `aitools
install/update/uninstall/list/version` at the top level. Hidden `skills
install` and `skills list` aliases for backward compat.

**Flags**:
- `--skills` (string, comma-separated) on install, update, uninstall:
operate on specific skills
- `--skills` (bool) on list, version: show detailed skills view
- `--agents` (string, comma-separated) on install: target specific
agents, validates against registry, skips interactive prompt
- `--include-experimental` on install: include experimental skills

**Selective uninstall**: `--skills` on uninstall removes only named
skills, preserves state file with remaining.

## Test plan

- [x] `install --skills`, `--agents`, `--include-experimental` flags
work
- [x] `--agents` validates against registry, errors on unknown
- [x] `uninstall --skills` selective removal, state preserved
- [x] `update --skills` selective update
- [x] `list` shows detailed table
- [x] `skills install` and `skills list` hidden aliases work (Execute
path tested)
- [x] `cmd/apps/init.go` integration preserved
- [x] All lint checks pass

## PR Stack

1. [1/5] State + release discovery + directory rename (#4810)
2. [2/5] Install writes state + interactive agent selection (#4811)
3. [3/5] Update + uninstall + version commands (#4812)
4. [4/5] List improvements + command restructuring + flags (#4813)
5. **[5/5] Project scope (--project/--global)** (this PR)

Manifest v2 PR: databricks/databricks-agent-skills#35

**Base**: `simonfaltum/aitools-pr4-restructure` (PR 4)

## Why

Skills are currently global-only. Teams working on the same project
can't share a curated set of skills via their repo. Project-scoped
installation puts skills alongside the code, so they can be committed to
git and shared.

## Changes

Before: All skills install to `~/.databricks/aitools/skills/` (global
only).

Now:
- `--project` flag on install, update, uninstall: operates on
`<cwd>/.databricks/aitools/skills/`
- `--global` flag: explicit global scope (default behavior)
- `--global` + `--project` -> error
- Interactive scope prompt on install (default: global). Uses
`huh.NewSelect` in cmd layer.
- Non-interactive defaults to global.
- `SupportsProjectScope` field on `Agent` struct. Only Claude Code and
Cursor support project scope.
- Incompatible agents get a warning, not an error: "Skipped <agent>:
does not support project-scoped skills."
- Version shows both scopes when both exist.
- State includes `scope: "project"` field for project installs.

## Test plan

- [x] `--project` installs to cwd-relative directory
- [x] `--global` + `--project` -> error
- [x] No flag, interactive -> scope prompt shown, default is global
- [x] No flag, non-interactive -> global (no prompt)
- [x] Incompatible agents warned, not errored
- [x] Symlinks only created for capable agents in project scope
- [x] Version shows both scopes when both exist
- [x] `SupportsProjectScope` set correctly for all 6 agents
- [x] All lint checks pass