feat(mcp): stream progress notifications for long-running tools

[unicoderbot]

Summary

Implement streaming MCP notifications/progress from long-running tools (test, packages_get, packages_check_licenses, create) so clients can show live progress while a command runs.

Changes

• Pass progressToken from request metadata to _runToolCommand()
• Emit notifications/progress messages as each line of command output is settled
• Use monotonically-increasing progress counter per MCP spec requirements
• Enhanced CapturingStdout to detect line boundaries (\n and \r) and invoke an optional onLine callback
• Progress notifications are fire-and-forget UX signals; the final tool result remains the source of truth
• Server stays silent when client omits progressToken (per MCP spec)

Details

• Added onLine parameter to CapturingStdout to report each settled, sanitized line as command output is captured
• \r boundaries (spinner redraws) are treated as settled-line boundaries so intermediate states surface
• Each progress notification includes the line's text as a human-readable message
• Initial "Starting" notification emitted immediately when token is provided
• Blank/whitespace-only lines are filtered out

Testing

• Verified progress notifications are not sent without a token
• Confirmed progress counter strictly increases across notifications
• Tested both string and integer token types
• Validated \r boundaries are detected and reported separately
• Confirmed all relevant tools emit progress when token is supplied

Closes #1616