Add --silent / -s flag to suppress row count output

[vmvarela]

Description

Add a --silent (-s) flag as the counterpart to --verbose (-v). When enabled, the number of rows processed is suppressed from stderr output, producing clean stdout-only output suitable for piping or scripting.

Acceptance Criteria

• --silent and -s are accepted as equivalent flags
• When --silent is set, the rows-processed count is not printed to stderr
• --silent and --verbose are mutually exclusive; passing both returns an error
• Help text (--help) documents --silent / -s alongside --verbose / -v
• Tests cover silent mode output and the mutually-exclusive conflict

Notes

• Rows processed is currently emitted by the --verbose path; silent mode should suppress it unconditionally regardless of whether -v is also absent
• No change to stdout (query results) — only stderr informational output is affected