deploy: combined opencode image + k8s + docs

- pilot/Dockerfile: python:3.12-slim + node 20 + opencode-ai@1.3.10 +
  ripgrep + pyright/typescript-language-server/eslint (npm) + ruff (pip).
  Factory + pilot scripts baked at /app. imagePullPolicy: Never (local
  import into microk8s containerd).
- .dockerignore: lean build context.
- ~/k8s/pragent-webhook.yaml: image pragent-webhook:opencode, emptyDir work
  at /tmp/pragent-work, env (PRAGENT_ENGINE, OPENCODE_MODEL, PRAGENT_FACTORY_DIR,
  PRAGENT_OPENCODE_BIN, PRAGENT_WORK_ROOT, PRAGENT_RTK_DIR='', timeout 540),
  resources 200m/512Mi -> 1500m/2Gi. Drops the ConfigMap scripts volume.
- pilot/README-webhook.md + .opencode/README.md: opencode engine section,
  build/import/apply steps, factory guide fixes (parse_review_output, steps).

Image builds (1.62GB, smoke-tested: opencode+LSPs+factory+env all present).
Import into microk8s containerd + apply pending (ctr needs sudo).

Co-Authored-By: Claude <noreply@anthropic.com>

.dockerignore

@@ -0,0 +1,12 @@
+.git
+.github
+__pycache__
+*.pyc
+tests
+*.jsonl
+*.token
+.env
+.pragent/cache/
+node_modules/
+dist/
+build/