Add command for deselecting site

[mtias]

We may want to explore allowing esc key while on site list to do this, but it may be too hidden

[wpmobilebot]

📊 Performance Test Results

Comparing 29b3dd6 vs trunk

app-size

Metric	trunk	29b3dd6	Diff	Change
App Size (Mac)	1236.62 MB	1236.63 MB	+0.00 MB	⚪ 0.0%

site-editor

Metric	trunk	29b3dd6	Diff	Change
load	1918 ms	1883 ms	35 ms	⚪ 0.0%

site-startup

Metric	trunk	29b3dd6	Diff	Change
siteCreation	7109 ms	6119 ms	990 ms	🟢 -13.9%
siteStartup	3925 ms	3923 ms	2 ms	⚪ 0.0%

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Results are median values from multiple test runs.

Legend: 🟢 Improvement (faster) | 🔴 Regression (slower) | ⚪ No change (<50ms diff)