fix(mobile): swallow blank-space terminal long presses

[DodgyBadger]

Summary

• Arm the terminal focus and compatibility-mouse guards before checking whether a long press landed on selectable text.
• Keep blank-space long presses marked for consumption so the existing touchend path suppresses Android Chrome's native behavior.
• Continue showing the selection, vibration, and Copy/Line toolbar only when a word was selected.
• Add CI-visible regression coverage for the blank-space path.

Fixes #360

Testing

• npm test -- test/terminal-touch-tap.test.ts (58 passed)
• npm test (7,828 passed, 12 skipped)
• npm run check:frontend-syntax
• npm run check:public-assets
• Manual Android Chrome test confirmed that long-pressing blank terminal space no longer blanks the viewport.

[Ark0N]

Merged, thanks @DodgyBadger! This ships in 1.32.1.

It is exactly the fix we sketched in #360: arm the focus and compat-mouse guards before asking whether the press landed on text, so a hold on blank space gets swallowed the same way a hold on a word already was. Small, and the regression test really does fail on master, which is what made this an easy merge with no changes on my side.

Two behaviour edges come with treating every 350 ms hold as a long press, both intended: a slow press on blank space no longer extends an existing selection (a quick tap still does), and a slow press on the blank tail of the prompt row no longer opens the keyboard. If either feels wrong on your phone, tell me and we tune it.