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/.env.example

@@ -5,11 +5,9 @@ PB_ADMIN_EMAIL=admin@example.com
 PB_ADMIN_PASSWORD=change-me-long-password
 
 # --- API Server -------------------------------------------------------------
-# Long random value used to sign auth tokens. Generate e.g.:
-#   openssl rand -hex 32
-AUTH_SECRET=change-me-to-a-long-random-value
 # Allowed CORS origin(s) for the web app (match WEB_PORT / your public URL).
-CORS_ORIGINS=http://localhost:8081
+# Native mobile apps are not subject to CORS.
+CORS_ALLOW_ORIGINS=http://localhost:8081
 AUTH_USERS_COLLECTION=users
 
 # --- Host port mappings (optional; defaults shown) --------------------------
@@ -18,5 +16,5 @@ API_PORT=8080
 WEB_PORT=8081
 
 # --- Web App build -----------------------------------------------------------
-# Leave empty so the browser uses same-origin /api (proxied by nginx).
+# Leave empty so the browser uses same-origin /api (proxied by the BFF).
 VITE_API_BASE=