refactor(skills): fold Integration skill lists into points of use

The list-style Integration sections in subagent-driven-development and
executing-plans duplicated references that already exist where the flow
uses them (process digraph, When to Use, prompt templates, Step 3), so
they added maintenance cost without carrying behavior. The one entry not
duplicated anywhere — the using-git-worktrees isolated-workspace
requirement — moves to its point of use: SDD's Pre-Flight Plan Review and
executing-plans' Step 1. Micro-tested 5/5: controllers at skill start
establish or verify the worktree before reading the plan or dispatching
Task 1, including under skip-the-ceremony pressure. The prose Integration
sections in requesting-code-review and other skills are unchanged — they
carry placement content, not an index.

skills/subagent-driven-development/SKILL.md

@@ -84,6 +84,9 @@ digraph process {
 
 ## Pre-Flight Plan Review
 
+Ensure the work happens in an isolated workspace: use
+superpowers:using-git-worktrees to create one or verify the existing one.
+
 Before dispatching Task 1, scan the plan once for conflicts:
 
 - tasks that contradict each other or the plan's Global Constraints
@@ -402,17 +405,3 @@ Done!
 **If subagent fails task:**
 - Dispatch fix subagent with specific instructions
 - Don't try to fix manually (context pollution)
-
-## Integration
-
-**Required workflow skills:**
-- **superpowers:using-git-worktrees** - Ensures isolated workspace (creates one or verifies existing)
-- **superpowers:writing-plans** - Creates the plan this skill executes
-- **superpowers:requesting-code-review** - Code review template for the final whole-branch review
-- **superpowers:finishing-a-development-branch** - Complete development after all tasks
-
-**Subagents should use:**
-- **superpowers:test-driven-development** - Subagents follow TDD for each task
-
-**Alternative workflow:**
-- **superpowers:executing-plans** - Use for parallel session instead of same-session execution