Add San — Go terminal-native AI agent runtime

[yanmxa]

Adds San to the Open Source terminal-native coding agents section.

Checklist against CONTRIBUTING:

• ✅ Has a CLI / terminal interface (terminal-native).
• ✅ Autonomously reads/writes code and runs commands (tool-using agent with permission modes).
• ✅ Link points to an active, valid project (latest release v2.0.1, Apache-2.0).
• ✅ Inserted in star-sorted order (45★, placed between QQCode 51★ and Smelt 21★).
• ✅ Single item, name + link + star count + one-line description + license.

San is a Go runtime for specialized AI agents: provider-agnostic (Anthropic, OpenAI, Google, DeepSeek, Moonshot, Qwen, MiniMax, GLM), runs Claude Code skills/plugins/MCP unmodified, with swappable search backends, custom personas, sandboxed subagents, lifecycle hooks, and a self-evolving memory loop. Ships as a single ~12 MB binary with zero runtime dependencies.