feat(vscode): expose /skills as slash command with secondary picker (#2548)

* feat(vscode): expose /skills as slash command with secondary picker

Add a secondary completion picker for the /skills slash command in the
VSCode IDE companion, allowing users to browse and select skills from
a dropdown before sending.

Changes:
- CLI: add 'skills' to ALLOWED_BUILTIN_COMMANDS_NON_INTERACTIVE whitelist
- CLI: send available_skills_update via ACP with skill names/descriptions
- Extension: handle available_skills_update in session update handler
- Webview: implement secondary picker that triggers after selecting /skills
- Webview: allow spaces in completion trigger for /skills sub-queries

Closes #1562

Made-with: Cursor

* feat(vscode-ide-companion): embed skills in commands update metadata

- Move available skills from separate session update to _meta field of
  available_commands_update for more efficient delivery
- Simplify skill data to just skill names (string array)
- Add skillsCompletion utility for secondary picker logic
- Cache available skills in WebViewProvider for replay on webview ready
- Update all related types and handlers to support the new structure

Co-authored-by: Qwen-Coder <qwen-coder@alibabacloud.com>

* refactor(vscode-ide-companion): simplify skills picker flow

* refactor(vscode-ide-companion): extract skills completion utils to shared module

Move `isSkillsSecondaryQuery`, `shouldOpenSkillsSecondaryPicker`, and
`SKILL_ITEM_ID_PREFIX` from App.tsx and useCompletionTrigger.ts into a
shared `completionUtils.ts` file to eliminate duplication.

* fix(vscode-ide-companion): restore skills picker state on reload

Cache and replay available skills when the webview becomes ready again.

Clear stale skills when commands metadata does not include availableSkills.

* fix(vscode-ide-companion): replay slash commands after webview reload

Cache available commands in the webview provider.

Replay them on webviewReady so slash command state survives reloads.

* fix(vscode-ide-companion): import AvailableCommand from ACP SDK

* fix(vscode-ide-companion): fallback /skills to direct command

* test(vscode-ide-companion): cover skills secondary picker flow

* test(vscode-ide-companion): guard App mock initialization

* fix(vscode-ide-companion): remove duplicate AvailableCommand import

The auto-merge introduced a duplicate AvailableCommand in the
@agentclientprotocol/sdk import block, causing TS2300.

* fix(vscode-ide-companion): remove duplicate availableCommands replay in handleWebviewReady

The handleWebviewReady method was sending cachedAvailableCommands twice
on every webview-ready handshake, causing an unnecessary extra state
update in the webview.

---------

Co-authored-by: Qwen-Coder <qwen-coder@alibabacloud.com>

.qwen/skills/structured-debugging/SKILL.md

@@ -187,8 +187,7 @@ Then apply the fix, remove instrumentation, and verify with a clean run.
 
 ## Worked examples
 
--
-  `examples/headless-bg-agent-empty-stdout.md`
+- `examples/headless-bg-agent-empty-stdout.md`
   — pipe-captured runs all passed; the user's TTY printed nothing. The
   contradiction _was_ the bug. Illustrates _reproduction contradiction is data_
   and _instrument data, not code paths_.