Add experiment ideas sections to all CRO skills

Adds curated A/B test experiments from SaaS CRO playbook to:
- page-cro: homepage, pricing, demo, resource page experiments
- signup-flow-cro: form design, copy, trial, post-submit experiments
- onboarding-cro: flow simplification, guided experience, personalization
- form-cro: structure, copy, mobile, type-specific experiments
- popup-cro: placement, triggers, messaging, personalization
- paywall-upgrade-cro: triggers, design, pricing, trials, personalization

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

skills/popup-cro.md

@@ -338,6 +338,97 @@ Ideas to A/B test with expected outcomes
 
 ---
 
+## Experiment Ideas
+
+### Placement & Format Experiments
+
+**Banner Variations**
+- Top bar vs. banner below header
+- Sticky banner vs. static banner
+- Full-width vs. contained banner
+- Banner with countdown timer vs. without
+
+**Popup Formats**
+- Center modal vs. slide-in from corner
+- Full-screen overlay vs. smaller modal
+- Bottom bar vs. corner popup
+- Top announcements vs. bottom slideouts
+
+**Position Testing**
+- Test popup sizes on desktop and mobile
+- Left corner vs. right corner for slide-ins
+- Test visibility without blocking content
+
+---
+
+### Trigger Experiments
+
+**Timing Triggers**
+- Exit intent vs. 30-second delay vs. 50% scroll depth
+- Test optimal time delay (10s vs. 30s vs. 60s)
+- Test scroll depth percentage (25% vs. 50% vs. 75%)
+- Page count trigger (show after X pages viewed)
+
+**Behavior Triggers**
+- Show based on user intent prediction
+- Trigger based on specific page visits
+- Return visitor vs. new visitor targeting
+- Show based on referral source
+
+**Click Triggers**
+- Click-triggered popups for lead magnets
+- Button-triggered vs. link-triggered modals
+- Test in-content triggers vs. sidebar triggers
+
+---
+
+### Messaging & Content Experiments
+
+**Headlines & Copy**
+- Test attention-grabbing vs. informational headlines
+- "Limited-time offer" vs. "New feature alert" messaging
+- Urgency-focused copy vs. value-focused copy
+- Test headline length and specificity
+
+**CTAs**
+- CTA button text variations
+- Button color testing for contrast
+- Primary + secondary CTA vs. single CTA
+- Test decline text (friendly vs. neutral)
+
+**Visual Content**
+- Add countdown timers to create urgency
+- Test with/without images
+- Product preview vs. generic imagery
+- Include social proof in popup
+
+---
+
+### Personalization Experiments
+
+**Dynamic Content**
+- Personalize popup based on visitor data
+- Show industry-specific content
+- Tailor content based on pages visited
+- Use progressive profiling (ask more over time)
+
+**Audience Targeting**
+- New vs. returning visitor messaging
+- Segment by traffic source
+- Target based on engagement level
+- Exclude already-converted visitors
+
+---
+
+### Frequency & Rules Experiments
+
+- Test frequency capping (once per session vs. once per week)
+- Cool-down period after dismissal
+- Test different dismiss behaviors
+- Show escalating offers over multiple visits
+
+---
+
 ## Questions to Ask
 
 If you need more context: