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.

.gitignore

@@ -53,3 +53,10 @@ Desktop.ini
 !/usb/cloudflare/SETUP.txt
 *.msi
 /cloudflared-windows-amd64.msi
+
+# Local build / test output (not tracked)
+/spread-kits/
+server/coverage/
+server/builder_cov/
+server/$cov/
+server/internal/builder/cov/