Clarify sqlcmd EOF troubleshooting and prefer bundled client in quickstart docs

[Copilot]

Users were hitting immediate EOF errors when running sqlcmd against a newly started container from Windows PowerShell. The docs did not clearly separate startup timing issues from host-shell quoting issues, and the quickest path still pointed at host sqlcmd.

• Quickstart path

  • Switch the homepage quickstart and getting-started flow to the bundled in-container sqlcmd first.
  • Add -b -l 2 to the initial query examples so early startup failures fail fast instead of looking ambiguous.

• Host sqlcmd guidance

  • Keep host sqlcmd as a secondary option after the bundled client succeeds.
  • Document the two common causes of immediate EOF in this scenario:
    • the engine is still initializing
    • PowerShell changed the -P argument while pasting, especially smart quotes or a leading space in the password

• Troubleshooting coverage

  • Add a dedicated EOF from host sqlcmd section to the container troubleshooting reference.
  • Explicitly tell users to verify with docker exec ... sqlcmd first, then retry the host client with the same short timeout.

docker exec sqldb /opt/mssql-tools18/bin/sqlcmd \
  -S localhost -U sa -P "YourStr0ng_Passw0rd" -C -b -l 2 \
  -Q "SELECT @@VERSION;"

sqlcmd -S localhost,1433 -U sa -P "YourStr0ng_Passw0rd" -C -b -l 2 \
  -Q "SELECT @@VERSION;"