refactor(skills): convert using-git-worktrees guard sections to rationalization table

Common Mistakes and Red Flags restated Steps 0-3 wholesale; both fold
into one Common Rationalizations table (house Excuse/Reality form) whose
five rows carry the tempting-thought version of each rule, including the
#1-mistake emphasis on bypassing native tools. Quick Reference stays as
the compact decision aid.

skills/using-git-worktrees/SKILL.md

@@ -156,47 +156,12 @@ Ready to implement <feature-name>
 | Tests fail during baseline | Report failures + ask |
 | No package.json/Cargo.toml | Skip dependency install |
 
-## Common Mistakes
-
-### Fighting the harness
-
-- **Problem:** Using `git worktree add` when the platform already provides isolation
-- **Fix:** Step 0 detects existing isolation. Step 1a defers to native tools.
-
-### Skipping detection
-
-- **Problem:** Creating a nested worktree inside an existing one
-- **Fix:** Always run Step 0 before creating anything
-
-### Skipping ignore verification
-
-- **Problem:** Worktree contents get tracked, pollute git status
-- **Fix:** Always use `git check-ignore` before creating project-local worktree
-
-### Assuming directory location
-
-- **Problem:** Creates inconsistency, violates project conventions
-- **Fix:** Follow priority: explicit instructions > existing project-local directory > default
-
-### Proceeding with failing tests
-
-- **Problem:** Can't distinguish new bugs from pre-existing issues
-- **Fix:** Report failures, get explicit permission to proceed
-
-## Red Flags
-
-**Never:**
-- Create a worktree when Step 0 detects existing isolation
-- Use `git worktree add` when you have a native worktree tool (e.g., `EnterWorktree`). This is the #1 mistake — if you have it, use it.
-- Skip Step 1a by jumping straight to Step 1b's git commands
-- Create worktree without verifying it's ignored (project-local)
-- Skip baseline test verification
-- Proceed with failing tests without asking
-
-**Always:**
-- Run Step 0 detection first
-- Prefer native tools over git fallback
-- Follow directory priority: explicit instructions > existing project-local directory > default
-- Verify directory is ignored for project-local
-- Auto-detect and run project setup
-- Verify clean test baseline
+## Common Rationalizations
+
+| Excuse | Reality |
+|--------|---------|
+| "I'm obviously not in a worktree — no need to check" | Run Step 0. Harness-created isolation and submodules both fool eyeballing; the detection commands settle it. |
+| "`git worktree add` is quicker than hunting for a native tool" | A native tool (e.g. `EnterWorktree`) owns placement, branching, and cleanup. Bypassing it is the #1 mistake — it creates phantom state your harness can't see or manage. |
+| "The worktree directory is surely ignored already" | Run `git check-ignore`. An unignored worktree directory commits the whole tree into the repo. |
+| "Any directory name works" | Explicit instructions beat an existing project-local directory, which beats the `.worktrees/` default. |
+| "The workspace is fresh — baseline tests can wait" | A dirty baseline makes every later failure ambiguous. Run the tests now; proceeding past failures is your human partner's call. |