fix: resolve all startup bugs (BUG-6 through BUG-9)

BUG-6: Add TLS support via axum-server + rustls
  - Added axum-server with tls-rustls feature to workspace and pm-web
  - pm-web now serves HTTPS when TLS certs exist, falls back to HTTP with warning
  - setup.sh generates self-signed ECDSA P-256 TLS cert with SANs
  - Config already had web_tls_cert_path/web_tls_key_path fields

BUG-7: Fix audit chain integrity errors
  - Migration 005 now TRUNCATEs audit_log after adding prev_hash column
  - Existing rows had broken hash chains (inserted before prev_hash existed)

BUG-8: Disable WatchdogSec in patch-manager-web.service
  - pm-web does not implement sd_notify, causing systemd to kill the service

BUG-9: Disable WatchdogSec in patch-manager-worker.service
  - Same issue as BUG-8, worker does not implement sd_notify

Previous fixes (BUG-1 through BUG-5) also included:
  - setup.sh: PostgreSQL 15+ schema GRANTs
  - Axum route syntax :param → {param} (19 routes)
  - DbUser struct role: String → UserRole enum mapping
  - UserRole/AuthProvider Display trait implementations
  - Seed admin password hash (Argon2id)

crates/pm-web/src/routes/maintenance_windows.rs

@@ -24,12 +24,12 @@ use crate::AppState;
 
 // ── Router ────────────────────────────────────────────────────────────────────
 
-/// Mount as a nested router under `/hosts/:host_id/maintenance-windows`.
-/// Axum will merge the `:host_id` path segment from the parent nest.
+/// Mount as a nested router under `/hosts/{host_id}/maintenance-windows`.
+/// Axum will merge the `{host_id}` path segment from the parent nest.
 pub fn router() -> Router<AppState> {
     Router::new()
         .route("/", get(list_windows).post(create_window))
-        .route("/:win_id", put(update_window).delete(delete_window))
+        .route("/{win_id}", put(update_window).delete(delete_window))
 }
 
 // ── Error helper ──────────────────────────────────────────────────────────────