Add regional task templates API with climate zone lookup

Adds a new endpoint GET /api/tasks/templates/by-region/?zip= that resolves
ZIP codes to IECC climate regions and returns relevant home maintenance
task templates. Includes climate region model, region lookup service with
tests, seed data for all 8 climate zones with 50+ templates, and OpenAPI spec.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

internal/handlers/task_template_handler.go

@@ -80,6 +80,24 @@ func (h *TaskTemplateHandler) GetTemplatesByCategory(c echo.Context) error {
 	return c.JSON(http.StatusOK, templates)
 }
 
+// GetTemplatesByRegion handles GET /api/tasks/templates/by-region/?state=XX or ?zip=12345
+// Returns templates specific to the user's climate region based on state abbreviation or ZIP code
+func (h *TaskTemplateHandler) GetTemplatesByRegion(c echo.Context) error {
+	state := c.QueryParam("state")
+	zip := c.QueryParam("zip")
+
+	if state == "" && zip == "" {
+		return apperrors.BadRequest("error.state_or_zip_required")
+	}
+
+	templates, err := h.templateService.GetByRegion(state, zip)
+	if err != nil {
+		return err
+	}
+
+	return c.JSON(http.StatusOK, templates)
+}
+
 // GetTemplate handles GET /api/tasks/templates/:id/
 // Returns a single template by ID
 func (h *TaskTemplateHandler) GetTemplate(c echo.Context) error {