fix(collections): trim 10104.ai-gateways.yml to 13 quality repos; remove conflicting 10105 and 10106

The original PR added 3 collection files with 1000+ repos each (mostly garbage).

Changes:
- configs/collections/10104.ai-gateways.yml: Trimmed from 1035 items down to
  13 high-quality, well-known AI gateway/proxy projects (all 500+ stars).
- configs/collections/10105.llm-gateways.yml: DELETED — ID 10105 conflicts with
  the existing mcp-servers.yml on main branch; content also overlaps with
  existing 10115.llm-gateway-proxy.yml collection.
- configs/collections/10106.mcp-gateways.yml: DELETED — ID 10106 conflicts with
  the existing coding-agents.yml on main branch; content overlaps with existing
  10099.mcp-client.yml and 10105.mcp-servers.yml collections.

Kept repos in 10104 (all verified 500+ stars, genuine AI gateway projects):
- alibaba/higress (7.9k stars)
- apache/apisix (16k stars)
- APIParkLab/APIPark (1.6k stars)
- agentgateway/agentgateway (2.1k stars)
- AmoyLab/Unla (2k stars) - MCP Gateway
- Azure-Samples/AI-Gateway (894 stars)
- BerriAI/litellm (40k stars)
- envoyproxy/ai-gateway (1.4k stars)
- Helicone/ai-gateway (557 stars)
- Kong/kong (43k stars)
- krakend/krakend-ce (2.5k stars)
- maximhq/bifrost (3.1k stars)
- Portkey-AI/gateway (11k stars)

Author: sykp241095