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>

Phone App/README.md

@@ -89,7 +89,7 @@ in Android Keystore–backed secure storage (`flutter_secure_storage`).
   On success the stored credentials are replayed against the normal login API, so
   each biometric sign-in mints a fresh session. Stale credentials (e.g. after a
   password change) auto-disable biometric login.
-- **App lock** — the JWT persists, so a valid session normally restores silently.
+- **App lock** — the token persists, so a valid session normally restores silently.
   When biometric login is enabled the app instead starts **locked** (and re-locks
   when backgrounded) and shows a lock screen requiring a biometric unlock. A
   **30-second grace period** means quick app-switches don't re-lock; a full app