WP-40/41/42: dashboard, security hardening, deployment and operations docs

Dashboard endpoint and page aggregating inventory, vulnerabilities, cluster
health, backups and recent jobs. Security headers (CSP, nosniff, DENY,
referrer policy), 1 MB body limit, configurable login rate limit, audit
steps in CI. Installer script, systemd unit, install/architecture docs.

Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>

docs/architecture.md

@@ -0,0 +1,27 @@
+# Architecture
+
+Single Rust binary (axum) serving the API and the built Vue SPA; SQLite for state; host tools
+(`apt-get`, `dpkg-query`, `snap`, `microk8s kubectl`, `trivy`, `smbclient`, `curl`, `tar`,
+`openssl`) are invoked as subprocesses behind ports so every use case is testable with fakes.
+
+```
+backend/crates/
+  domain/          entities, validation, ports (traits)        no I/O
+  application/     use cases: auth, users, settings, jobs,     depends on domain
+                   scheduler, inventory, upgrade, cluster,
+                   vulnerabilities, backups
+  infrastructure/  SQLite repos, Argon2/JWT/AES-GCM, lettre,   implements the ports
+                   Debian inspector/updater, kube-rs gateway,
+                   Trivy, smbclient/curl storage, collectors
+  api/             axum routes, auth extractors, OpenAPI,      wires everything
+                   security headers, config, main
+frontend/          Vue 3 + TypeScript + Tailwind, Pinia stores, Playwright e2e
+```
+
+Cross-cutting: a `JobRunner` executes long-running work (refresh, upgrade, scan, backup) as
+persisted job runs with live logs; a `Scheduler` ticks every 30 s and starts due jobs from cron
+expressions (settings) and backup strategies. Secrets at rest are AES-256-GCM encrypted with
+`MASTER_KEY`. Authentication: Argon2id passwords, 15-minute JWT access tokens, rotating refresh
+tokens in an HttpOnly, SameSite=Strict cookie scoped to `/api/auth`, reuse detection revokes the
+token family. `FAKE_HOST=true` swaps all host/cluster/scanner/storage adapters for fakes so the
+app runs on a developer machine and in the UI tests.