Add webhook logging, pagination, middleware, migrations, and prod hardening

- Webhook event logging repo and subscription webhook idempotency
- Pagination helper (echohelpers) with cursor/offset support
- Request ID and structured logging middleware
- Push client improvements (FCM HTTP v1, better error handling)
- Task model version column, business constraint migrations, targeted indexes
- Expanded categorization chain tests
- Email service and config hardening
- CI workflow updates, .gitignore additions, .env.example updates

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

internal/middleware/logger.go

@@ -0,0 +1,53 @@
+package middleware
+
+import (
+	"time"
+
+	"github.com/labstack/echo/v4"
+	"github.com/rs/zerolog/log"
+
+	"github.com/treytartt/casera-api/internal/models"
+)
+
+// StructuredLogger is zerolog-based request logging middleware that includes
+// correlation IDs, user IDs, and latency metrics.
+func StructuredLogger() echo.MiddlewareFunc {
+	return func(next echo.HandlerFunc) echo.HandlerFunc {
+		return func(c echo.Context) error {
+			start := time.Now()
+
+			err := next(c)
+
+			latency := time.Since(start)
+
+			// Build structured log event
+			event := log.Info()
+			if c.Response().Status >= 500 {
+				event = log.Error()
+			} else if c.Response().Status >= 400 {
+				event = log.Warn()
+			}
+
+			// Request ID
+			if reqID := GetRequestID(c); reqID != "" {
+				event = event.Str("request_id", reqID)
+			}
+
+			// User ID (from auth middleware)
+			if user, ok := c.Get(AuthUserKey).(*models.User); ok && user != nil {
+				event = event.Uint("user_id", user.ID)
+			}
+
+			event.
+				Str("method", c.Request().Method).
+				Str("path", c.Path()).
+				Str("uri", c.Request().RequestURI).
+				Int("status", c.Response().Status).
+				Int64("latency_ms", latency.Milliseconds()).
+				Str("remote_ip", c.RealIP()).
+				Msg("request")
+
+			return err
+		}
+	}
+}