feat: feedback submissions with screenshots, the hide-widget preference and its user payload key

- POST /_feedback/api/v1/{key}/submit validates as PHP, refuses non-image screenshots (ImageContentGuard copy) and stores the submission, its public screenshot and the G15Office job in one transaction
- PUT /_feedback/api/v1/me/hidden (jwt.auth) stores the caller's preference; feedback_widget_hidden joins every golem15.user payload
- preflights stay with the framework CORS layer

classes/sync_g15office.go

@@ -0,0 +1,22 @@
+package classes
+
+// The G15Office sync job's contract: SubmitFeedback queues one per stored
+// submission, the worker files it (SyncFeedbackToG15Office).
+const (
+	// SyncG15OfficeKind is the River kind of the job.
+	SyncG15OfficeKind = "golem15.feedback.sync_g15office"
+	// SyncG15OfficeQueue is the job's queue.
+	SyncG15OfficeQueue = "feedback"
+	// SyncG15OfficeLabel is the summer_jobs label, the PHP job class.
+	SyncG15OfficeLabel = `Golem15\Feedback\Jobs\SyncFeedbackToG15Office`
+	// SyncG15OfficeAttempts is SyncFeedbackToG15Office::$tries.
+	SyncG15OfficeAttempts = 3
+)
+
+// SyncG15OfficeArgs is the job's argument: the submission to file.
+type SyncG15OfficeArgs struct {
+	SubmissionID uint `json:"submission_id"`
+}
+
+// Kind is the River job kind.
+func (SyncG15OfficeArgs) Kind() string { return SyncG15OfficeKind }