refactor: Separate CV domain and UI presentation models into distinct packages

**Main Changes:**

1. **Package Restructuring** - Separated mixed concerns into focused packages:
   - Created `internal/models/cv/` for CV domain logic (CV, Personal, Experience, etc.)
   - Created `internal/models/ui/` for UI presentation logic (InfoModal, ShortcutsModal, etc.)
   - Removed monolithic `internal/models/cv.go` (300+ lines → organized packages)

2. **Testing** - Added comprehensive unit tests:
   - `internal/models/cv/loader_test.go` - CV data loading and validation
   - `internal/models/ui/loader_test.go` - UI translations loading
   - All tests passing ✅

3. **Documentation** - Added Go learning knowledge base:
   - `_go-learning/architecture/server-design.md` - Goroutines, graceful shutdown explained
   - `_go-learning/refactorings/001-cv-model-separation.md` - This refactoring documented
   - Public documentation showcasing Go expertise (README.md kept private)

4. **Handler Updates** - Updated imports to use new package structure:
   - `internal/handlers/cv.go` - Uses `cvmodel` and `uimodel` aliases

**Benefits:**
- ✅ Clear separation of concerns (domain vs presentation)
- ✅ Better testability (isolated package testing)
- ✅ Improved maintainability (smaller, focused files)
- ✅ Scalability (each domain can evolve independently)
- ✅ Follows Go best practices (small, cohesive packages)

**Other Updates:**
- Updated middleware security checks
- Template improvements
- Organized completed prompts

**Testing:**
- All Go unit tests pass (cv, ui, handlers)
- Server verified with curl tests (English, Spanish, Health endpoints)
- Frontend functionality unchanged (refactoring is transparent to UI)

internal/handlers/cv.go

@@ -11,7 +11,8 @@ import (
 	"strings"
 	"time"
 
-	"github.com/juanatsap/cv-site/internal/models"
+	cvmodel "github.com/juanatsap/cv-site/internal/models/cv"
+	uimodel "github.com/juanatsap/cv-site/internal/models/ui"
 	"github.com/juanatsap/cv-site/internal/pdf"
 	"github.com/juanatsap/cv-site/internal/templates"
 )
@@ -53,14 +54,14 @@ func (h *CVHandler) Home(w http.ResponseWriter, r *http.Request) {
 	}
 
 	// Load CV data
-	cv, err := models.LoadCV(lang)
+	cv, err := cvmodel.LoadCV(lang)
 	if err != nil {
 		HandleError(w, r, DataLoadError(err, "CV"))
 		return
 	}
 
 	// Load UI translations
-	ui, err := models.LoadUI(lang)
+	ui, err := uimodel.LoadUI(lang)
 	if err != nil {
 		HandleError(w, r, DataLoadError(err, "UI"))
 		return
@@ -161,14 +162,14 @@ func (h *CVHandler) CVContent(w http.ResponseWriter, r *http.Request) {
 	}
 
 	// Load CV data
-	cv, err := models.LoadCV(lang)
+	cv, err := cvmodel.LoadCV(lang)
 	if err != nil {
 		HandleError(w, r, DataLoadError(err, "CV"))
 		return
 	}
 
 	// Load UI translations
-	ui, err := models.LoadUI(lang)
+	ui, err := uimodel.LoadUI(lang)
 	if err != nil {
 		HandleError(w, r, DataLoadError(err, "UI"))
 		return
@@ -345,7 +346,7 @@ func (h *CVHandler) ExportPDF(w http.ResponseWriter, r *http.Request) {
 	log.Printf("PDF export requested: lang=%s, length=%s, icons=%s, version=%s", lang, length, icons, version)
 
 	// Load CV data to get name for filename
-	cv, err := models.LoadCV(lang)
+	cv, err := cvmodel.LoadCV(lang)
 	if err != nil {
 		HandleError(w, r, DataLoadError(err, "CV"))
 		return
@@ -441,7 +442,7 @@ func (h *CVHandler) ExportPDF(w http.ResponseWriter, r *http.Request) {
 
 // splitSkills splits skill categories between left (page 1) and right (page 2) sidebars
 // Each category explicitly specifies which sidebar it belongs to via the "sidebar" field
-func splitSkills(skills []models.SkillCategory) (left, right []models.SkillCategory) {
+func splitSkills(skills []cvmodel.SkillCategory) (left, right []cvmodel.SkillCategory) {
 	if len(skills) == 0 {
 		return nil, nil
 	}
@@ -570,7 +571,7 @@ func calculateDuration(startDate, endDate string, current bool, lang string) str
 // processProjectDates calculates dynamic dates for projects
 // If a project has a gitRepoUrl, it fetches the first commit date
 // For current projects, it sets the current system date
-func processProjectDates(project *models.Project, lang string) {
+func processProjectDates(project *cvmodel.Project, lang string) {
 	now := time.Now()
 
 	// Set dynamic current date for ongoing projects
@@ -718,13 +719,13 @@ func getGitRepoFirstCommitDate(repoPath string) string {
 // prepareTemplateData prepares common template data used across handlers
 func (h *CVHandler) prepareTemplateData(lang string) (map[string]interface{}, error) {
 	// Load CV data
-	cv, err := models.LoadCV(lang)
+	cv, err := cvmodel.LoadCV(lang)
 	if err != nil {
 		return nil, err
 	}
 
 	// Load UI translations
-	ui, err := models.LoadUI(lang)
+	ui, err := uimodel.LoadUI(lang)
 	if err != nil {
 		return nil, err
 	}