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>

Web App/.dockerignore

@@ -0,0 +1,17 @@
+# Keep the build context small and avoid leaking local artifacts/secrets.
+.env
+*.log
+*.exe
+*.exe~
+
+# Frontend deps + generated output — rebuilt inside the image.
+web/node_modules/
+web/dist/
+server/dist/
+
+# VCS / editor / tooling noise
+.git/
+.gitignore
+.claude/
+.vscode/
+.idea/