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.

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

AGENTS.md

@@ -28,6 +28,7 @@ Dev stack: Postgres on `:15432` (`containr-postgres-1`), Dragonfly on `:16379` (
 ## Conventions that matter
 
 - New endpoints go in the right route group; mutations on `authed`/`admin` get idempotency for free.
+- Deploy work goes through `deploy_queue` (`internal/deployqueue`) — per-service FIFO; enqueue jobs instead of `go`-ing deployment/reconcile goroutines so they never race a build.
 - New list endpoints use `pageWindow`/`paginationMeta` (`internal/api/pagination.go`) — cursor + page, `next_cursor` in the envelope.
 - New errors use stable codes via `respondError(c, status, code, msg)` in `internal/api/errors.go`.
 - New CLI command → also register an MCP tool in `internal/mcpserver/server.go` and document in OpenAPI. All three surfaces ship together.