feat: add 20 new practical skills (65→86 total)

20 production-ready skills for professional Claude Code users.

Engineering (12): git-worktree-manager, ci-cd-pipeline-builder, mcp-server-builder, changelog-generator, pr-review-expert, api-test-suite-builder, env-secrets-manager, database-schema-designer, codebase-onboarding, performance-profiler, runbook-generator, monorepo-navigator

Engineering Team (2): stripe-integration-expert, email-template-builder
Product (3): saas-scaffolder, landing-page-generator, competitive-teardown  
Business (1): contract-and-proposal-writer
Marketing (1): prompt-engineer-toolkit
AI Engineering (1): agent-workflow-designer

Also: README updated (badges, counts, new section), STORE.md (Stan Store + Gumroad distribution plan)

engineering/git-worktree-manager/SKILL.md

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+# Git Worktree Manager
+
+**Tier:** POWERFUL  
+**Category:** Engineering  
+**Domain:** Parallel Development & Branch Isolation
+
+## Overview
+
+The Git Worktree Manager skill provides systematic management of Git worktrees for parallel development workflows. It handles worktree creation with automatic port allocation, environment file management, secret copying, and cleanup — enabling developers to run multiple Claude Code instances on separate features simultaneously without conflicts.
+
+## Core Capabilities
+
+- **Worktree Lifecycle Management** — create, list, switch, and cleanup worktrees with automated setup
+- **Port Allocation & Isolation** — automatic port assignment per worktree to avoid dev server conflicts
+- **Environment Synchronization** — copy .env files, secrets, and config between main and worktrees
+- **Docker Compose Overrides** — generate per-worktree port override files for multi-service stacks
+- **Conflict Prevention** — detect and warn about shared resources, database names, and API endpoints
+- **Cleanup & Pruning** — safe removal with stale branch detection and uncommitted work warnings
+
+## When to Use This Skill
+
+- Running multiple Claude Code sessions on different features simultaneously
+- Working on a hotfix while a feature branch has uncommitted work
+- Reviewing a PR while continuing development on your branch
+- Parallel CI/testing against multiple branches
+- Monorepo development with isolated package changes
+
+## Worktree Creation Workflow
+
+### Step 1: Create Worktree
+
+```bash
+# Create worktree for a new feature branch
+git worktree add ../project-feature-auth -b feature/auth
+
+# Create worktree from an existing remote branch
+git worktree add ../project-fix-123 origin/fix/issue-123
+
+# Create worktree with tracking
+git worktree add --track -b feature/new-api ../project-new-api origin/main
+```
+
+### Step 2: Environment Setup
+
+After creating the worktree, automatically:
+
+1. **Copy environment files:**
+   ```bash
+   cp .env ../project-feature-auth/.env
+   cp .env.local ../project-feature-auth/.env.local 2>/dev/null
+   ```
+
+2. **Install dependencies:**
+   ```bash
+   cd ../project-feature-auth
+   [ -f "pnpm-lock.yaml" ] && pnpm install
+   [ -f "yarn.lock" ] && yarn install
+   [ -f "package-lock.json" ] && npm install
+   [ -f "bun.lockb" ] && bun install
+   ```
+
+3. **Allocate ports:**
+   ```
+   Main worktree:     localhost:3000 (dev), :5432 (db), :6379 (redis)
+   Worktree 1:        localhost:3010 (dev), :5442 (db), :6389 (redis)
+   Worktree 2:        localhost:3020 (dev), :5452 (db), :6399 (redis)
+   ```
+
+### Step 3: Docker Compose Override
+
+For Docker Compose projects, generate per-worktree override:
+
+```yaml
+# docker-compose.worktree.yml (auto-generated)
+services:
+  app:
+    ports:
+      - "3010:3000"
+  db:
+    ports:
+      - "5442:5432"
+  redis:
+    ports:
+      - "6389:6379"
+```
+
+Usage: `docker compose -f docker-compose.yml -f docker-compose.worktree.yml up`
+
+### Step 4: Database Isolation
+
+```bash
+# Option A: Separate database per worktree
+createdb myapp_feature_auth
+
+# Option B: DATABASE_URL override
+echo 'DATABASE_URL="postgresql://localhost:5442/myapp_wt1"' >> .env.local
+
+# Option C: SQLite — file-based, automatic isolation
+```
+
+## Monorepo Optimization
+
+Combine worktrees with sparse checkout for large repos:
+
+```bash
+git worktree add --no-checkout ../project-packages-only
+cd ../project-packages-only
+git sparse-checkout init --cone
+git sparse-checkout set packages/shared packages/api
+git checkout feature/api-refactor
+```
+
+## Claude Code Integration
+
+Each worktree gets auto-generated CLAUDE.md:
+
+```markdown
+# Worktree: feature/auth
+# Dev server port: 3010
+# Created: 2026-03-01
+
+## Scope
+Focus on changes related to this branch only.
+
+## Commands
+- Dev: PORT=3010 npm run dev
+- Test: npm test -- --related
+- Lint: npm run lint
+```
+
+Run parallel sessions:
+```bash
+# Terminal 1: Main feature
+cd ~/project && claude
+# Terminal 2: Hotfix
+cd ~/project-hotfix && claude
+# Terminal 3: PR review
+cd ~/project-pr-review && claude
+```
+
+## Common Pitfalls
+
+1. **Shared node_modules** — Worktrees share git dir but NOT node_modules. Always install deps.
+2. **Port conflicts** — Two dev servers on :3000 = silent failures. Always allocate unique ports.
+3. **Database migrations** — Migrations in one worktree affect all if sharing same DB. Isolate.
+4. **Git hooks** — Live in `.git/hooks` (shared). Worktree-specific hooks need symlinks.
+5. **IDE confusion** — VSCode may show wrong branch. Open as separate window.
+6. **Stale worktrees** — Prune regularly: `git worktree prune`.
+
+## Best Practices
+
+1. Name worktrees by purpose: `project-auth`, `project-hotfix-123`, `project-pr-456`
+2. Never create worktrees inside the main repo directory
+3. Keep worktrees short-lived — merge and cleanup within days
+4. Use the setup script — manual creation skips env/port/deps
+5. One Claude Code instance per worktree — isolation is the point
+6. Commit before switching — even WIP commits prevent lost work