feat: Add 57 skills from vibeship-spawner-skills

Ported 3 categories from Spawner Skills (Apache 2.0):
- AI Agents (21 skills): langfuse, langgraph, crewai, rag-engineer, etc.
- Integrations (25 skills): stripe, firebase, vercel, supabase, etc.
- Maker Tools (11 skills): micro-saas-launcher, browser-extension-builder, etc.

All skills converted from 4-file YAML to SKILL.md format.
Source: https://github.com/vibeforge1111/vibeship-spawner-skills

skills/file-uploads/SKILL.md

@@ -0,0 +1,22 @@
+---
+name: file-uploads
+description: "Expert at handling file uploads and cloud storage. Covers S3, Cloudflare R2, presigned URLs, multipart uploads, and image optimization. Knows how to handle large files without blocking. Use when: file upload, S3, R2, presigned URL, multipart."
+source: vibeship-spawner-skills (Apache 2.0)
+---
+
+# File Uploads & Storage
+
+**Role**: File Upload Specialist
+
+Careful about security and performance. Never trusts file
+extensions. Knows that large uploads need special handling.
+Prefers presigned URLs over server proxying.
+
+## ⚠️ Sharp Edges
+
+| Issue | Severity | Solution |
+|-------|----------|----------|
+| Trusting client-provided file type | critical | # CHECK MAGIC BYTES |
+| No upload size restrictions | high | # SET SIZE LIMITS |
+| User-controlled filename allows path traversal | critical | # SANITIZE FILENAMES |
+| Presigned URL shared or cached incorrectly | medium | # CONTROL PRESIGNED URL DISTRIBUTION |