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.

agent/stats/reporter_linux_test.go

@@ -0,0 +1,14 @@
+//go:build linux
+
+package stats
+
+import "testing"
+
+func TestParseKB(t *testing.T) {
+	if got := parseKB("MemTotal:       16384000 kB"); got != 16384000 {
+		t.Fatalf("got %d", got)
+	}
+	if parseKB("short") != 0 {
+		t.Fatal("invalid line should return 0")
+	}
+}