Friendly duplicate-name errors on create/edit

UNIQUE constraint violations from rack/device/model creation and editing
now show readable messages like 'A rack named X already exists, onii-chan'
instead of raw SQLite error strings or silent redirects.

internal/handlers/devices.go

@@ -3,6 +3,7 @@ package handlers
 import (
 	"net/http"
 	"strconv"
+	"strings"
 
 	"lostcavewireplanner/internal/models"
 )
@@ -84,7 +85,11 @@ func (h *Handlers) DeviceCreate(w http.ResponseWriter, r *http.Request) {
 
 	id, err := h.Store.DeviceCreate(device)
 	if err != nil {
-		h.redirect(w, r, "/")
+		msg := err.Error()
+		if strings.Contains(strings.ToLower(msg), "unique") {
+			msg = "A device named '" + name + "' already exists, onii-chan."
+		}
+		renderDeviceCreateError(h, w, msg)
 		return
 	}
 

internal/handlers/models.go

@@ -84,7 +84,11 @@ func (h *Handlers) ModelCreate(w http.ResponseWriter, r *http.Request) {
 
 	_, err := h.Store.ModelCreate(m, "uploads")
 	if err != nil {
-		h.render(w, "model_form.html", ModelFormData{Model: m, IsEdit: false, Error: err.Error()})
+		msg := err.Error()
+		if strings.Contains(strings.ToLower(msg), "unique") {
+			msg = "A model named '" + m.Name + "' already exists, onii-chan."
+		}
+		h.render(w, "model_form.html", ModelFormData{Model: m, IsEdit: false, Error: msg})
 		return
 	}
 
@@ -138,7 +142,11 @@ func (h *Handlers) ModelUpdate(w http.ResponseWriter, r *http.Request) {
 	}
 
 	if err := h.Store.ModelUpdate(m); err != nil {
-		h.render(w, "model_form.html", ModelFormData{Model: m, IsEdit: true, Error: err.Error()})
+		msg := err.Error()
+		if strings.Contains(strings.ToLower(msg), "unique") {
+			msg = "A model named '" + m.Name + "' already exists, onii-chan."
+		}
+		h.render(w, "model_form.html", ModelFormData{Model: m, IsEdit: true, Error: msg})
 		return
 	}
 

internal/handlers/overview.go

@@ -3,6 +3,7 @@ package handlers
 import (
 	"net/http"
 	"strconv"
+	"strings"
 
 	"lostcavewireplanner/internal/models"
 )
@@ -86,7 +87,11 @@ func (h *Handlers) RackCreate(w http.ResponseWriter, r *http.Request) {
 	}
 	_, err := h.Store.RackCreate(rack)
 	if err != nil {
-		h.renderError(w, "overview.html", err.Error())
+		msg := err.Error()
+		if strings.Contains(strings.ToLower(msg), "unique") {
+			msg = "A rack with this name already exists, onii-chan."
+		}
+		h.renderError(w, "overview.html", msg)
 		return
 	}
 	h.redirect(w, r, "/")
@@ -133,3 +138,7 @@ func (h *Handlers) renderError(w http.ResponseWriter, page string, errMsg string
 		http.Error(w, errMsg, http.StatusBadRequest)
 	}
 }
+
+func renderDeviceCreateError(h *Handlers, w http.ResponseWriter, errMsg string) {
+	renderOverviewError(h, w, errMsg)
+}

internal/handlers/racks.go

@@ -146,7 +146,11 @@ func (h *Handlers) RackEdit(w http.ResponseWriter, r *http.Request) {
 	rack.Comment = r.FormValue("comment")
 
 	if err := h.Store.RackUpdate(rack); err != nil {
-		h.renderRackError(w, *rack, "Failed to update: "+err.Error())
+		msg := err.Error()
+		if strings.Contains(strings.ToLower(msg), "unique") {
+			msg = "A rack named '" + rack.Name + "' already exists, onii-chan."
+		}
+		h.renderRackError(w, *rack, msg)
 		return
 	}
 	h.redirect(w, r, "/racks/"+idStr)