Add example servers for SEP-2053 variant patterns (#4)

Add four new example servers demonstrating different SEP-2053 variant
patterns:

- model-optimized (same tools, different descriptions per LLM family)
- trading (API versioning with deprecation lifecycle)
- research (context budget management)
- Refactor the existing variants-http example into a GitHub-style server
with custom ranking.

Signed-off-by: Kurt Degiorgio <kdegiorgio@bloomberg.net>

README.md

@@ -13,6 +13,34 @@ This repository provides a multi-language reference implementation of the varian
 | TypeScript | `typescript/sdk/` | `@ext-modelcontextprotocol/variants` | Planned |
 
 
+## Examples (Go)
+
+The Go implementation includes runnable example servers under [`go/sdk/examples/server/`](go/sdk/examples/server/):
+
+### [`model-optimized/`](go/sdk/examples/server/model-optimized/)
+
+Same tools, different descriptions per LLM family.
+
+https://github.com/user-attachments/assets/5bb60cd2-291f-4940-abfe-f53852d35470
+
+### [`github/`](go/sdk/examples/server/github/)
+
+Different tool sets per variant with custom ranking.
+
+https://github.com/user-attachments/assets/d770ac55-e988-4d89-bdf8-bcb3cf1e2e53
+
+### [`research/`](go/sdk/examples/server/research/)
+
+Context budget management via description verbosity.
+
+### [`trading/`](go/sdk/examples/server/trading/)
+
+API versioning, lifecycle statuses, and deprecation info.
+
+### [`variants-stdio/`](go/sdk/examples/server/variants-stdio/)
+
+Minimal single-variant setup.
+
 ## CI/CD
 
 This monorepo uses **path-based CI workflows** to efficiently test only what changes: