fix(skills): point skel references at ${CLAUDE_PLUGIN_ROOT}/skel, drop local-machine paths

setup SKILL.md referenced the developer machine's plugin checkout for the
customizations starter pack and ship-check.py scaffold, so first-run setup
failed on every external install. Both now resolve from the packaged skel/
directory; the ship-check copy gains an existence guard so an unset
CLAUDE_PLUGIN_ROOT degrades to a no-op instead of a hard cp error.
execute-task prose pointer updated to match.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
(cherry picked from commit f5df447)

Author: claude

skills/execute-task/SKILL.md

@@ -256,7 +256,7 @@ The termination sequence is strict — three steps, in order, no shortcuts:
    false-positive matches by log-watchers.
 
 The ship-check script is deterministic. Its gates are documented at the
-top of `~/Shade_Gen/Projects/prd-taskmaster-plugin/.atlas-ai-skel/ship-check.py`:
+top of `${CLAUDE_PLUGIN_ROOT}/skel/ship-check.py` (copied to `.atlas-ai/ship-check.py` at setup):
 
 - Gate 1: `pipeline.json current_phase == "EXECUTE"`
 - Gate 2: every `master.tasks[].status == "done"`

skills/setup/SKILL.md

@@ -83,7 +83,7 @@ no recovery path.
 This step ensures the file exists BEFORE execute-task ever runs:
 
 ```bash
-PLUGIN_SKEL="$HOME/Shade_Gen/Projects/prd-taskmaster-plugin/.atlas-ai-skel/customizations"
+PLUGIN_SKEL="${CLAUDE_PLUGIN_ROOT}/skel/customizations"
 mkdir -p .atlas-ai/customizations
 if [ ! -f .atlas-ai/customizations/system-prompt-template.md ]; then
   if [ -d "$PLUGIN_SKEL" ]; then
@@ -102,8 +102,8 @@ file simply must exist.
 Also scaffold `.atlas-ai/ship-check.py` if it doesn't already exist:
 
 ```bash
-if [ ! -f .atlas-ai/ship-check.py ]; then
-  cp "$HOME/Shade_Gen/Projects/prd-taskmaster-plugin/.atlas-ai-skel/ship-check.py" .atlas-ai/ship-check.py
+if [ ! -f .atlas-ai/ship-check.py ] && [ -f "${CLAUDE_PLUGIN_ROOT}/skel/ship-check.py" ]; then
+  cp "${CLAUDE_PLUGIN_ROOT}/skel/ship-check.py" .atlas-ai/ship-check.py
   chmod +x .atlas-ai/ship-check.py
 fi
 ```