feat: add plugin worker protocol, bootstrap and plugin_storage table

Worker-side ctx proxy plus the message envelope it talks over, and the
per-plugin key/value table behind ctx.storage with migrations for all
three dialects. Rows cascade with the plugin so uninstalling leaves
nothing behind.

drizzle/sqlite/meta/_journal.json

@@ -148,6 +148,13 @@
       "when": 1789751454932,
       "tag": "0020_moaning_fat_cobra",
       "breakpoints": true
+    },
+    {
+      "idx": 21,
+      "version": "6",
+      "when": 1789991403283,
+      "tag": "0021_dashing_lester",
+      "breakpoints": true
     }
   ]
 }