Fix README: update binary name, fix docs, add missing flags

- Replace all ./scanner references with findns
- Fix go build -o scanner → go build -o findns
- Fix incorrect claim that dnstt-client must be in PATH only
  (findns searches PATH, current dir, and next to executable)
- Add missing --e2e-timeout to global flags tables (EN + FA)
- Add missing --proxy-auth to scan flags tables (EN + FA)
- Add missing --port-base to chain command docs (EN + FA)
- Add missing cert param to e2e/slipstream chain step (EN + FA)

Author: SamNet-dev