feat(deploy): per-service deploy queue, cancellable deployments, no-cache builds

- internal/deployqueue: serialized FIFO per service — concurrent deploys
  of one service no longer race (the container-name-conflict failure
  mode); different services still run in parallel.
- Deploys and rollbacks enqueue through the queue; a busy service
  returns status 'queued' and promotes when the active job finishes.
- POST /deployments/:id/cancel — queued jobs drop immediately
  (200 cancelled); active jobs get ctx cancelled so build/reconcile
  abort (202 cancelling, settles 'cancelled'); finished deployments
  return 409 NOT_CANCELLABLE.
- Redeploy and variables save now route through the same queue so they
  can't overlap a build; PUT /services/:id/variables accepts
  redeploy:true to apply env changes to running containers.
- no_cache on deployment create plumbs BuildRequest -> BuildOptions for
  nixpacks, dockerfile and railpack builders.
- CLI: deployments cancel, deploy --no-cache, variables set/unset
  --redeploy. MCP: containr_deployments_cancel; deploy/variables_set
  document no_cache/redeploy. UI: Cancel button + queued/cancelled
  badges on the deployments table. OpenAPI + types regenerated.

Generated with [Devin](https://devin.ai)

Co-Authored-By: Devin <158243242+devin-ai-integration[bot]@users.noreply.github.com>

app/backend/internal/api/routes.go

@@ -10,6 +10,7 @@ import (
 	"containr/internal/config"
 	"containr/internal/database"
 	"containr/internal/deployment"
+	"containr/internal/deployqueue"
 	"containr/internal/docker"
 	"containr/internal/ha"
 	"containr/internal/metrics"
@@ -98,6 +99,10 @@ func SetupRoutes(router *gin.Engine, db *database.DB, redis *database.Redis, cfg
 	// Initialize database handler
 	databaseHandler := NewDatabaseHandler(db.DB, dockerClient)
 
+	// Per-service serialized deploy queue — one active deployment per
+	// service, the rest wait as 'queued'.
+	deployQueue := deployqueue.New()
+
 	// Initialize security handler
 	securityHandler := NewSecurityHandler(db, cfg.JWTSecret)
 
@@ -115,6 +120,7 @@ func SetupRoutes(router *gin.Engine, db *database.DB, redis *database.Redis, cfg
 		if deploymentEngine != nil {
 			c.Set("deployment_engine", deploymentEngine)
 		}
+		c.Set("deploy_queue", deployQueue)
 		c.Set("scheduler", scheduler)
 		c.Set("metrics_collector", metricsCollector)
 		c.Set("auto_scaler", autoScaler)
@@ -289,6 +295,7 @@ func SetupRoutes(router *gin.Engine, db *database.DB, redis *database.Redis, cfg
 			authed.POST("/services/:id/redeploy", handleServiceRedeploy)
 			authed.POST("/services/:id/deployments", handleCreateDeployment)
 			authed.POST("/deployments/:id/rollback", handleRollbackDeployment)
+			authed.POST("/deployments/:id/cancel", handleCancelDeployment)
 
 			// Environment variables — secrets, owner/admin only.
 			authed.GET("/services/:id/variables", handleGetVariables)