docs: soften Step 1a native-tool framing per PR #1121 review

Address obra's comment on explicit step numbers / prescriptive tone.
Drops "STOP HERE if available", the "If YES:" gate, and the "even if /
even if / NO EXCEPTIONS" reinforcement paragraph. Keeps the specific
tool-name anchors (EnterWorktree, WorktreeCreate, /worktree, --worktree),
which the original TDD data showed are load-bearing.

A/B verified against drill harness on the 3 creation/consent scenarios
(consent-flow, creation-from-main, creation-from-main-spec-aware):
baseline explicit wording scored 12/12 criteria, softened wording also
scored 12/12. The "agent used the most appropriate tool" criterion
passed in all 3 softened runs — agents still picked EnterWorktree via
ToolSearch without the imperative framing.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

skills/using-git-worktrees/SKILL.md

@@ -48,15 +48,13 @@ Honor any existing declared preference without asking. If the user declines cons
 
 **You have two mechanisms. Try them in this order.**
 
-### 1a. Native Worktree Tools (preferred — STOP HERE if available)
+### 1a. Native Worktree Tools (preferred)
 
-The user has asked for an isolated workspace (Step 0 consent). Check your available tools — do you have `EnterWorktree`, `WorktreeCreate`, a `/worktree` command, or a `--worktree` flag? **If YES: the user's consent to create a worktree is your authorization to use it. Use it now and skip to Step 3.**
+The user has asked for an isolated workspace (Step 0 consent). Do you already have a way to create a worktree? It might be a tool with a name like `EnterWorktree`, `WorktreeCreate`, a `/worktree` command, or a `--worktree` flag. If you do, use it and skip to Step 3.
 
-Native tools handle directory placement, branch creation, and cleanup automatically. Using `git worktree add` when you have a native tool creates phantom state — your harness can't see or manage worktrees it didn't create, and cleanup becomes impossible.
+Native tools handle directory placement, branch creation, and cleanup automatically. Using `git worktree add` when you have a native tool creates phantom state your harness can't see or manage.
 
-**Even if `.worktrees/` already exists, even under time pressure, even if `git worktree add` feels faster — use your native tool.** There are no exceptions.
-
-**Only proceed to Step 1b if you have confirmed you have NO native worktree/isolation tool.**
+Only proceed to Step 1b if you have no native worktree tool available.
 
 ### 1b. Git Worktree Fallback