refactor: upgrade to Go 1.26 and modernize code idioms

- Replace `interface{}` with `any` type alias across all packages
- Use built-in `min()`/`max()` for parameter clamping
- Use `slices.SortFunc`, `slices.Min`, `slices.Max` for cleaner code
- Use `strings.Cut()` for simpler string parsing in auth middleware
- Use `errors.Is()` for proper error comparison in handlers
- Update dependencies: golang.org/x/image 0.37.0 -> 0.38.0
- Add Wire code generation guidelines to ARCHITECTURE.md
- Disable Go cache in CI build workflow

internal/pkg/openai/client.go

@@ -210,8 +210,8 @@ type responseFormatConfig struct {
 }
 
 type chatMessage struct {
-	Role    string      `json:"role"`
-	Content interface{} `json:"content"`
+	Role    string `json:"role"`
+	Content any    `json:"content"`
 }
 
 type contentPart struct {