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/router/router.go

@@ -339,6 +339,7 @@ func setupPublicDataRoutes(api *echo.Group, residenceHandler *handlers.Residence
 		templates.GET("/grouped/", taskTemplateHandler.GetTemplatesGrouped)
 		templates.GET("/search/", taskTemplateHandler.SearchTemplates)
 		templates.GET("/by-category/:category_id/", taskTemplateHandler.GetTemplatesByCategory)
+		templates.GET("/by-region/", taskTemplateHandler.GetTemplatesByRegion)
 		templates.GET("/:id/", taskTemplateHandler.GetTemplate)
 	}
 }