fix(electric): stop restarting Electric on unrelated deploys - #1457

🟢 Confidence 8/10 · likely safe to merge
The pin moves unchanged into ELECTRIC_IMAGE; the only unverifiable step is alchemy 2.0.0-beta.83 mirroring a bare image ref to ECR, which the next prd deploy itself proves.
_{quality 100/100 · no findings · tests not needed · risk medium}

Electric stops being built from a Dockerfile context and is instead handed to the ECS service as the same pinned ghcr ref, so a bun.lock change no longer retags it and restarts the singleton. The pin, the workflow summary and the runbook stay consistent; safe to merge.

• ELECTRIC_IMAGE in apps/electric/alchemy.run.ts replaces the context+Dockerfile build, keeping the same digest pin
• AWS.ECS.Service("electric") now takes image instead of context/dockerfile
• apps/electric/Dockerfile deleted; the publish workflow and docs/electric-sync.md point at ELECTRIC_IMAGE

Before merge

• Infra · Check every environment has what this config now expects · apps/electric/alchemy.run.ts

_{ed590bc · Updated on every push. Reply "won't fix" to dismiss a finding, or mention @maple-review-bot to ask about one.}