Default to half-screen mode when opening with certain CLI args

[jesseduffield]

It should have been half-screen from the get-go. I think I just used full-screen to make demos look nicer. Now that we have a CLI arg for the screen mode we can make use of that in the demos.

Relates to #3042

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Coverage summary from Codacy

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Coverage variation	Diff coverage
Report missing for 536ef821	✅ 100.00%

Coverage variation details

	Coverable lines	Covered lines	Coverage
Common ancestor commit (536ef82)	Report Missing	Report Missing	Report Missing
Head commit (621229b)	51539	44527	86.39%

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Diff coverage details

	Coverable lines	Covered lines	Diff coverage
Pull request (#4141)	1	1	100.00%

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