feat: ship docker as a first-party in-process plugin

Moves docker backend and frontend into plugins/docker/, alongside
ssh-terminal. Adds a host editor tab seam, a dashboard card registry,
and a build step to compile plugin backends into dist.

.gitignore

@@ -13,6 +13,14 @@ dist-ssr
 coverage
 *.local
 
+# tsc -p tsconfig.plugins.json emits plugin backend .js next to its .ts
+# source. It also stray-emits sibling .js next to every core .ts the plugin
+# imports for type-checking (src/types, src/backend/utils, repositories...);
+# scripts/copy-bundled-plugins.cjs removes those after every compile, this
+# is a safety net for running tsc -p tsconfig.plugins.json directly.
+/plugins/*/backend/*.js
+/src/**/*.js
+
 .vscode/*
 !.vscode/settings.json
 .idea