feat: add co-marketing skill (#289)

* feat: add co-marketing skill for partner identification and joint campaigns

Adds skill for finding co-marketing partners and brainstorming campaign ideas:
- Partner scoring criteria and identification framework
- Campaign types (content, webinars, integrations, community)
- Outreach templates and partnership structuring
- Brainstorming prompts for specific partners

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

* docs: add co-marketing to README skills table and categories

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

* docs: add co-marketing to README diagram

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

* fix: improve co-marketing skill based on review

- Add quoted description with expanded trigger phrases
- Add metadata.version field (1.0.0)
- Add "Before Starting" section for product context
- Add Task-Specific Questions section
- Add Tool Integrations section (Crossbeam, Introw, PartnerStack)
- Add Co-Marketing Checklist (identification, planning, execution, post-campaign)
- Clarify Related Skills with better context
- Add horizontal rules for section separation (matches other skills)

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

---------

Co-authored-by: Claude Opus 4.5 <noreply@anthropic.com>

VERSIONS.md

@@ -44,9 +44,14 @@ Current versions of all skills. Agents can compare against local versions to che
 | social-content | 1.3.0 | 2026-04-24 |
 | image | 1.0.0 | 2026-04-24 |
 | video | 1.0.0 | 2026-04-24 |
+| co-marketing | 1.0.0 | 2026-05-04 |
 
 ## Recent Changes
 
+### 2026-05-04
+- Added `co-marketing` skill for partner identification, joint campaigns, and co-marketing strategy
+- Total skills: 41
+
 ### 2026-04-24
 - Added `image` skill for AI image generation, design tools, profile/listing banners, and optimization
 - Added `video` skill for AI video production (Hyperframes, HeyGen, Veo, Runway, Kling)