feat(preview): real preview environments — clone, deploy, TTL, promote (#67)

Preview environments were bookkeeping only: a fabricated deployment row
marked "running" and a fake *.preview.containr.local URL. Now a preview
is a real service clone — full config copy (source, env, volumes, access),
git_branch pinned to the requested branch, its own preview hostname under
the clone's node default domain, and a real deployment through the queue.

- cloneServiceRow extracted from handleCloneService for reuse
- preview_environments.preview_service_id links to the clone
- minute sweeper: expires past-TTL previews (removes clone runtime + row)
  and syncs preview status from the clone's live service status
- delete/cleanup paths tear the clone down, not just the row
- promote redeploys the SOURCE service at the preview branch and retires
  the clone — a real deployment, not a pending stub

Verified live: create → clone → deploy → running container; TTL expiry →
clone + container gone; promote → real deploy on the source, preview
stopped. Unit test covers the DNS-safe clone naming.

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

ROADMAP2.md

@@ -520,8 +520,9 @@ and wired refs, one click or one CLI call.
 - [x] **Gateway traffic path** — `/g/:slug/*` mounted → api_key auth →
   rpm + monthly quota → `gateway/proxy.go` → usage_counters /
   metrics_timeseries / incident_events.
-- [ ] **Preview environments runtime** — real build+deploy+subdomain+TTL
-  (bookkeeping only now). Pairs with clone + multi-domain.
+- [x] **Preview environments runtime** — previews are real service clones:
+  branch override, queued deployment, node-domain hostnames, TTL sweeper,
+  promote = redeploy of the source at the preview branch.
 - [ ] **Environments** — env switcher, per-env vars/domains, promote.
 - [ ] **sqlc port** — ~140 raw `database/sql` sites → `sqlc/queries/`.
 - [ ] **Tests** — canvas/wizard frontend coverage, deployment/template/