feat: ops layer — incidents, maintenance, status pages, badges, metrics (merge plan M4)

incidents + incident_updates + maintenance_windows + status_pages
tables. Monitor transitions auto-open incidents on down and
auto-resolve on recovery; an active maintenance window covering
the monitor suppresses alerts and auto-incidents, and status
pages report the covered monitor as `maintenance`.

Public status view: GET /api/status-pages/:slug/public aggregates
overall state, monitor uptime, systems, open incidents, and
scheduled maintenance; rendered read-only at /status/:slug.

GET /api/badge/:kind/:id.svg serves stateless shields; GET
/api/metrics exposes Prometheus text over existing tables;
POST /api/import/csv?kind=monitors|domains does header-driven
bulk import; /api/export v2 folds monitors/domains/systems rows
into the backup payload.

Frontend: /incidents with timeline + status flow, /status admin
for pages + windows, /status/:slug public page; nav and palette
wired.

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

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

apps/backend/internal/db/migrations/0006_ops.sql

@@ -0,0 +1,45 @@
+-- +goose Up
+CREATE TABLE incidents (
+    id         TEXT PRIMARY KEY,
+    title      TEXT NOT NULL,
+    severity   TEXT NOT NULL DEFAULT 'major',   -- minor | major | critical
+    status     TEXT NOT NULL DEFAULT 'open',    -- open | ack | resolved | closed
+    monitor_id TEXT REFERENCES monitors(id) ON DELETE SET NULL,
+    created_at TEXT NOT NULL DEFAULT (strftime('%Y-%m-%dT%H:%M:%fZ','now')),
+    updated_at TEXT NOT NULL DEFAULT (strftime('%Y-%m-%dT%H:%M:%fZ','now'))
+);
+CREATE INDEX idx_incidents_status ON incidents(status);
+
+CREATE TABLE incident_updates (
+    id          INTEGER PRIMARY KEY AUTOINCREMENT,
+    incident_id TEXT NOT NULL REFERENCES incidents(id) ON DELETE CASCADE,
+    status      TEXT NOT NULL,
+    message     TEXT NOT NULL DEFAULT '',
+    at          TEXT NOT NULL DEFAULT (strftime('%Y-%m-%dT%H:%M:%fZ','now'))
+);
+CREATE INDEX idx_incident_updates_inc ON incident_updates(incident_id);
+
+CREATE TABLE maintenance_windows (
+    id          TEXT PRIMARY KEY,
+    title       TEXT NOT NULL,
+    starts_at   TEXT NOT NULL,
+    ends_at     TEXT NOT NULL,
+    monitor_ids TEXT NOT NULL DEFAULT '[]',  -- JSON array; empty covers all
+    created_at  TEXT NOT NULL DEFAULT (strftime('%Y-%m-%dT%H:%M:%fZ','now'))
+);
+
+CREATE TABLE status_pages (
+    id          TEXT PRIMARY KEY,
+    slug        TEXT NOT NULL UNIQUE,
+    title       TEXT NOT NULL,
+    description TEXT NOT NULL DEFAULT '',
+    monitor_ids TEXT NOT NULL DEFAULT '[]',  -- JSON array; empty = all monitors
+    system_ids  TEXT NOT NULL DEFAULT '[]',
+    created_at  TEXT NOT NULL DEFAULT (strftime('%Y-%m-%dT%H:%M:%fZ','now'))
+);
+
+-- +goose Down
+DROP TABLE IF EXISTS status_pages;
+DROP TABLE IF EXISTS maintenance_windows;
+DROP TABLE IF EXISTS incident_updates;
+DROP TABLE IF EXISTS incidents;