Expand test coverage across server, agent, and web; fix bugs found during audit.

Adds hundreds of unit/integration/e2e tests, fixes WS bcrypt auth, config merge, fleet analytics, agent schedule/log tail, and documents stale PROBLEMS items. Updates PROBLEMS.md, README, and test scripts; ignores local spread-kits and coverage dirs.

server/internal/builder/limits_test.go

@@ -0,0 +1,15 @@
+package builder
+
+import "testing"
+
+func TestFusionConstants(t *testing.T) {
+	if FusionMaxUploadBytes != 2<<30 {
+		t.Fatalf("FusionMaxUploadBytes: got %d want %d", FusionMaxUploadBytes, 2<<30)
+	}
+	if FusionDeliverablesDir != "fusion-deliverables" {
+		t.Fatalf("FusionDeliverablesDir: got %q", FusionDeliverablesDir)
+	}
+	if mediaLockMagic != "CMVD" {
+		t.Fatalf("mediaLockMagic: got %q", mediaLockMagic)
+	}
+}