When the sqlserver command failed to connect, the tool printed the same
generic message twice and hid the real SqlException. Now:

- Surface SqlException Number, State, Class, Server, and all errors in
  the failure message
- Echo the effective connection identity (Data Source, Initial Catalog,
  Integrated Security, Windows identity) before probing, never secrets
- Unwrap HaltException to the innermost exception when printing and
  dedupe repeated messages
- Always write a redacted diagnostics log file (full exception chain,
  Password/PWD blanked) and report wrapped errors, including with
  --unattended
- Harden --connectionStringSource parsing: trim whitespace, strip
  wrapping quotes, and validate each line, reporting the 1-based line
  number on parse failure