feat: rename 15 skills for shorter, cleaner names

Renames:
- ab-test-setup → ab-testing
- analytics-tracking → analytics
- competitor-alternatives → competitors
- email-sequence → emails
- free-tool-strategy → free-tools
- launch-strategy → launch
- onboarding-cro → onboarding
- paywall-upgrade-cro → paywalls
- popup-cro → popups
- pricing-strategy → pricing
- product-marketing-context → product-marketing
- referral-program → referrals
- schema-markup → schema
- signup-flow-cro → signup
- social-content → social

Updates all cross-references in skills, references, tools,
marketplace.json, README, AGENTS.md, and CONTRIBUTING.md.

BREAKING: Users with installed skills will need to reinstall.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

skills/social/references/platform-limits.md

@@ -0,0 +1,110 @@
+# Platform Limits Reference
+
+Quick reference for hashtag limits, character counts, and visible text thresholds on each major social platform.
+
+---
+
+## Instagram
+
+| Element | Limit |
+|---------|-------|
+| Max hashtags | 5 (official limit) |
+| Recommended hashtags | 3 – 5 |
+| Max caption chars | 2,200 |
+| Visible before "more" | ~125 chars |
+
+---
+
+## Facebook
+
+| Element | Limit |
+|---------|-------|
+| Max hashtags | No official limit |
+| Recommended hashtags | 1 – 2 |
+| Max post chars | 63,206 |
+| Ideal for engagement | 40 – 80 chars |
+
+---
+
+## TikTok
+
+| Element | Limit |
+|---------|-------|
+| Max hashtags | 5 (since August 2025) |
+| Recommended hashtags | 3 – 5 |
+| Max caption chars | 4,000 |
+| Visible before "more" | ~150 chars |
+
+---
+
+## LinkedIn
+
+| Element | Limit |
+|---------|-------|
+| Max hashtags | No official limit |
+| Recommended hashtags | 3 – 5 |
+| Max post chars | 3,000 |
+| Visible before "more" | ~210 chars |
+
+---
+
+## Twitter/X
+
+| Element | Limit |
+|---------|-------|
+| Max hashtags | No official limit |
+| Recommended hashtags | 1 – 2 |
+| Max tweet chars | 280 (standard) / 25,000 (Premium+) |
+| Visible before "more" | Full tweet (280 standard) |
+
+---
+
+## YouTube
+
+| Element | Limit |
+|---------|-------|
+| Max hashtags | 15 (exceeding this causes YouTube to ignore ALL hashtags) |
+| Recommended hashtags | 3 – 5 |
+| Max title chars | 100 (visible before truncation: ~70) |
+| Max description chars | 5,000 |
+| Visible before "Show more" | ~100 chars |
+
+> The first 3 hashtags in the description automatically appear above the title as clickable links. For Shorts, use 1 – 5 hashtags.
+
+---
+
+## Pinterest
+
+| Element | Limit |
+|---------|-------|
+| Max hashtags | 20 per pin |
+| Recommended hashtags | 2 – 5 |
+| Max pin title chars | 100 |
+| Max description chars | 500 |
+| Visible before "More" | ~50 chars (desktop) |
+
+> Pinterest has deprioritized hashtags. Focus on keywords as natural sentences within the description for better SEO instead of relying on hashtags.
+
+---
+
+## Threads (Meta)
+
+| Element | Limit |
+|---------|-------|
+| Max hashtags | 1 per post (topic tag) |
+| Recommended hashtags | 1 |
+| Max post chars | 500 |
+| Max with text attachment | 10,500 (500 + 10,000 expandable) |
+| Visible without expanding | First ~1 – 2 lines |
+
+> Threads limits topic tags to one per post. The platform is not hashtag-driven — the algorithm prioritizes content from followed accounts mixed with recommendations.
+
+---
+
+## Usage Tips
+
+- **Hashtags count against character limits** on all platforms
+- **Front-load your message** before the "more" truncation point
+- On Instagram and TikTok, fewer hashtags now outperform hashtag-stuffing
+- On LinkedIn, hashtags at the end of the post perform better than inline
+- On Facebook, hashtags have minimal impact on reach — use sparingly