Warn loudly at startup if handoff_project_status doesn't exist on project

Root cause of the re-dispatch loop: WORKFLOW.md configured
handoff_project_status: "Human Review" but the GitHub Project only has
status options [Todo, In Progress, Done]. No "Human Review" option exists.

Result: UpdateProjectField silently skipped (empty HandoffOptionID),
project status stayed "In Progress" (still in active_values), items
re-dispatched endlessly even after PR creation.

Fix: At startup, after loading project metadata, verify the configured
handoff status exists in the project's status options. If not, emit a
prominent stderr warning with available options and how to fix it.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: shivamstaq

cmd/symphony/main.go

@@ -175,6 +175,21 @@ func main() {
 				"field_id", meta.FieldID,
 				"options", len(meta.Options),
 			)
+			// Verify the handoff status option exists
+			if _, ok := meta.Options[cfg.PullRequest.HandoffProjectStatus]; !ok {
+				available := make([]string, 0, len(meta.Options))
+				for name := range meta.Options {
+					available = append(available, name)
+				}
+				logger.Error("CRITICAL: handoff_project_status not found in project",
+					"configured", cfg.PullRequest.HandoffProjectStatus,
+					"available_options", available,
+				)
+				fmt.Fprintf(os.Stderr, "\n⚠️  WARNING: handoff_project_status %q does not exist on your GitHub Project.\n", cfg.PullRequest.HandoffProjectStatus)
+				fmt.Fprintf(os.Stderr, "   Available status options: %v\n", available)
+				fmt.Fprintf(os.Stderr, "   Symphony cannot move items to handoff status after PR creation.\n")
+				fmt.Fprintf(os.Stderr, "   Fix: add %q to your project's Status field, or change handoff_project_status in WORKFLOW.md\n\n", cfg.PullRequest.HandoffProjectStatus)
+			}
 		}
 	}