feat(api): phase 5 — alerts, agent depth, subdomains, auth, boards

P5b: notifier transport registry (webhook/slack/discord/telegram/
gotify/ntfy/smtp via net/smtp), per-monitor+domain alert rules
(failsBeforeDown, latencyWarn, certDays, mute).

P5c: per-container cpu/mem, optional SMART/ZFS/GPU exec-or-skip
collectors, crt.sh subdomain discovery with daily sweep.

P5d: opt-in auth (bcrypt, sqlite sessions, 7d rotating cookie, login
rate limit, public-route bypass) and multiple boards (boards table,
sections.board_id, /api/boards CRUD, slug routing).

Authored By: TDvorak <[email protected]>

Generated with [Devin](https://devin.ai)

Co-Authored-By: Devin <158243242+devin-ai-integration[bot]@users.noreply.github.com>

apps/backend/internal/monitor/monitor.go

@@ -42,6 +42,7 @@ type Monitor struct {
 	PushToken     string    `json:"pushToken,omitempty"`
 	Tags          []string  `json:"tags"`
 	Notes         string    `json:"notes"`
+	Alerts        json.RawMessage `json:"alerts"`
 	Position      float64   `json:"position"`
 	LastCheck     *string   `json:"lastCheck"`
 	CreatedAt     string    `json:"createdAt"`