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/request_id.go

@@ -0,0 +1,43 @@
+package middleware
+
+import (
+	"github.com/google/uuid"
+	"github.com/labstack/echo/v4"
+)
+
+const (
+	// HeaderXRequestID is the header key for request correlation IDs
+	HeaderXRequestID = "X-Request-ID"
+	// ContextKeyRequestID is the echo context key for the request ID
+	ContextKeyRequestID = "request_id"
+)
+
+// RequestIDMiddleware generates a UUID per request, sets it as X-Request-ID header,
+// and stores it in the echo context for downstream use.
+func RequestIDMiddleware() echo.MiddlewareFunc {
+	return func(next echo.HandlerFunc) echo.HandlerFunc {
+		return func(c echo.Context) error {
+			// Use existing request ID from header if present, otherwise generate one
+			reqID := c.Request().Header.Get(HeaderXRequestID)
+			if reqID == "" {
+				reqID = uuid.New().String()
+			}
+
+			// Store in context
+			c.Set(ContextKeyRequestID, reqID)
+
+			// Set response header
+			c.Response().Header().Set(HeaderXRequestID, reqID)
+
+			return next(c)
+		}
+	}
+}
+
+// GetRequestID extracts the request ID from the echo context
+func GetRequestID(c echo.Context) string {
+	if id, ok := c.Get(ContextKeyRequestID).(string); ok {
+		return id
+	}
+	return ""
+}