chore: remove Electric SQL plumbing and infrastructure

Remove all Electric SQL client code, Docker service, env vars, CI build
args, install scripts, and documentation. Feature hooks that depend on
Electric are intentionally left in place to be rewritten with Rocicorp
Zero in subsequent commits.

Deleted:
- lib/electric/ (client.ts, context.ts, auth.ts, baseline.ts)
- ElectricProvider.tsx
- docker/scripts/init-electric-user.sh
- content/docs/how-to/electric-sql.mdx

Cleaned:
- package.json (4 @electric-sql/* deps)
- app/layout.tsx, UserDropdown.tsx, LayoutDataProvider.tsx
- docker-compose.yml, docker-compose.dev.yml
- Dockerfile, docker-entrypoint.js
- .env.example (frontend, docker, backend)
- CI workflows, install scripts, docs

surfsense_web/components/UserDropdown.tsx

@@ -16,7 +16,6 @@ import {
 } from "@/components/ui/dropdown-menu";
 import { Spinner } from "@/components/ui/spinner";
 import { logout } from "@/lib/auth-utils";
-import { cleanupElectric } from "@/lib/electric/client";
 import { resetUser, trackLogout } from "@/lib/posthog/events";
 
 export function UserDropdown({
@@ -39,14 +38,6 @@ export function UserDropdown({
 			trackLogout();
 			resetUser();
 
-			// Best-effort cleanup of Electric SQL / PGlite
-			// Even if this fails, login-time cleanup will handle it
-			try {
-				await cleanupElectric();
-			} catch (err) {
-				console.warn("[Logout] Electric cleanup failed (will be handled on next login):", err);
-			}
-
 			// Revoke refresh token on server and clear all tokens from localStorage
 			await logout();