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)

systemd/patch-manager-web.service

@@ -29,8 +29,8 @@ StartLimitBurst=5
 TimeoutStartSec=90s
 TimeoutStopSec=30s
 
-# Watchdog — pm-web must report health within this interval
-WatchdogSec=120s
+# Watchdog disabled — pm-web does not currently implement sd_notify
+# WatchdogSec=120s
 
 # Security hardening
 NoNewPrivileges=true

systemd/patch-manager-worker.service

@@ -29,8 +29,8 @@ StartLimitBurst=5
 TimeoutStartSec=120s
 TimeoutStopSec=120s
 
-# Watchdog — worker must report heartbeat within this interval
-WatchdogSec=180s
+# Watchdog disabled — pm-worker does not currently implement sd_notify
+# WatchdogSec=180s
 
 # Security hardening
 NoNewPrivileges=true