Refresh docs and fix Docker builds for current layout

READMEs: correct the auth model (PocketBase token relay, not JWT/sessions),
document the full feature set (technical checks, fuel, maintenance, documents,
reminders, attachments, integrations, OCPP charging control), the shipping
built-in connectors (toyota, anker-solix), and the current endpoint surface.

Docker: build against the current repo layout — Go 1.26, cmd/server entry
point, Web App source under web/. Add the missing Web App Dockerfile (Go BFF)
and .dockerignore, drop the obsolete AUTH_SECRET, modernise CORS var naming,
and standardise on drivervault-* naming.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

Docker AIO/.env.example

@@ -4,8 +4,6 @@
 # PocketBase superuser, also used by the API Server to authenticate.
 PB_ADMIN_EMAIL=admin@example.com
 PB_ADMIN_PASSWORD=change-me-long-password
-# Signs auth tokens. Generate e.g.: openssl rand -hex 32
-AUTH_SECRET=change-me-to-a-long-random-value
 
 # --- Host port mappings (optional; defaults shown) --------------------------
 WEB_PORT=80