feat: upgrade to Go 1.25.3 and update build to include api-gateway

- Create ADR-0034 documenting Go version upgrade to 1.25.3
- Mark ADR-0002 as superseded by ADR-0034
- Update CI workflow to use Go 1.25.3
- Update Makefile to build both platform and api-gateway binaries
- Update CI workflow to build and upload both binaries
- Update documentation (ADR README and mkdocs.yml) to include ADR-0034

.github/workflows/ci.yml

@@ -17,7 +17,7 @@ jobs:
       - name: Set up Go
         uses: actions/setup-go@v5
         with:
-          go-version: '1.24'
+          go-version: '1.25.3'
 
       - name: Cache Go modules
         uses: actions/cache@v4
@@ -76,7 +76,7 @@ jobs:
       - name: Set up Go
         uses: actions/setup-go@v5
         with:
-          go-version: '1.24'
+          go-version: '1.25.3'
 
       - name: Install golangci-lint v2.1.6
         run: |
@@ -96,7 +96,7 @@ jobs:
       - name: Set up Go
         uses: actions/setup-go@v5
         with:
-          go-version: '1.24'
+          go-version: '1.25.3'
 
       - name: Cache Go modules
         uses: actions/cache@v4
@@ -110,13 +110,17 @@ jobs:
         run: go mod download
 
       - name: Build
-        run: go build -v -o bin/platform ./cmd/platform
+        run: |
+          go build -v -o bin/platform ./cmd/platform
+          go build -v -o bin/api-gateway ./cmd/api-gateway
 
       - name: Upload build artifacts
         uses: actions/upload-artifact@v3
         with:
-          name: platform-binary
-          path: bin/platform
+          name: binaries
+          path: |
+            bin/platform
+            bin/api-gateway
           retention-days: 7
 
   fmt:
@@ -129,7 +133,7 @@ jobs:
       - name: Set up Go
         uses: actions/setup-go@v5
         with:
-          go-version: '1.24'
+          go-version: '1.25.3'
 
       - name: Check formatting
         run: |