fix(release): close the 0.19.0 scan findings — sandbox mongo tag, flow-verb timeout walls, video hardening (#329)

- mongo:8-alpine → mongo:8 (tag never existed; a mongo-opted project could spawn no agents) + a Docker Hub tag-existence e2e guard for every sandbox engine
- flow-verb timeouts at both walls: shared SLOW_VERBS policy (i_am_done / submit_up / submit_root / open_pr / i_will_work_on get the 900s server budget); the MCP client now outlasts the server budget (+10s headroom, orchestrator-injected env) so agents receive the middleware's clean 504 envelope instead of dying at the old flat 30s client timeout
- cancellation safety: the quality gate kills+reaps its child on CancelledError; create_pr records the PR via a shield-with-wait-out helper so the write can neither be skipped nor race get_db's rollback
- video engine: renderer sidecar isolated on a render-only network, 2g/2cpu caps, 570s render watchdog with exit-on-hang, 512MB tar decompression cap, CEO notification on terminal render failure, reject under the approve mutex (fail-closed on Redis-down)
- dead python-jose dependency removed (drops ecdsa and its unfixable Minerva advisory PYSEC-2026-1325); panel --font-mono now a real monospace stack

Co-authored-by: Renn F <rennf93@users.noreply.github.com>

panel/src/app/globals.css

@@ -8,7 +8,8 @@
   --color-background: var(--background);
   --color-foreground: var(--foreground);
   --font-sans: var(--font-inter);
-  --font-mono: var(--font-inter);
+  --font-mono:
+    ui-monospace, "SF Mono", Menlo, Consolas, "Liberation Mono", monospace;
   --color-sidebar-ring: var(--sidebar-ring);
   --color-sidebar-border: var(--sidebar-border);
   --color-sidebar-accent-foreground: var(--sidebar-accent-foreground);