fix(ci): update backend Go version from 1.24 to 1.26.1 (#337)

Align the CI backend job with the Go version declared in server/go.mod
and used in the Dockerfile (golang:1.26-alpine).

Co-authored-by: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

.github/workflows/ci.yml

@@ -57,7 +57,7 @@ jobs:
       - name: Setup Go
         uses: actions/setup-go@v5
         with:
-          go-version: "1.24"
+          go-version: "1.26.1"
           cache-dependency-path: server/go.sum
 
       - name: Build

CLAUDE.md

@@ -149,7 +149,7 @@ make db-down          # Stop shared PostgreSQL
 
 ### CI Requirements
 
-CI runs on Node 22 and Go 1.24 with a `pgvector/pgvector:pg17` PostgreSQL service. See `.github/workflows/ci.yml`.
+CI runs on Node 22 and Go 1.26.1 with a `pgvector/pgvector:pg17` PostgreSQL service. See `.github/workflows/ci.yml`.
 
 ### Worktree Support