[addhumal]

Closes #279 and #280. Sill's controls can now be swiped away so the picture gets the screen. Upright, the picture grows into the room they leave.

How it works

• Sideways: a swipe up on the bar hides it, and the picture fills the screen.
• Upright, iPhone or iPad:
  • A swipe down on the rows hides the trackpad. The picture grows into its room, and the viewport follows, so the Mac fits the window to the taller picture (Use the freed room: the picture grows when the trackpad is hidden #280).
  • A second swipe down hides the rest.
  • A swipe up on the rows brings the trackpad back.
• The way back:
  • With everything hidden, a swipe in from the edge the controls left brings them all back: the top sideways, the bottom upright. Sill takes that swipe ahead of iOS's own.
  • A small grabber shows at that edge for 2 s after hiding, and it's a button.
• VoiceOver: "Show Sill's controls" on the picture, and "Hide Sill's controls" and "Show the trackpad" on the rows.
• Which swipe: it starts on the controls, never on the picture, where one finger belongs to the Mac. It must be 40 pt and twice as far up or down as across, so the thumbnail strip's sideways scroll is no swipe.
• Nothing hides while the app drawer, Settings or Aa's ruler is open. Turned sideways with only the trackpad hidden, the bar shows (it has no trackpad).
• The rules are HiddenControls: pure, in PhonePortraitLayout.swift. DEBUG: -SillHideControls trackpad|all.
• This builds on main, not on Stream: Hide Top Bar in landscape, shake to show it again (#92) #197 (Hide Top Bar, shake) or Immersive: the stream edge to edge on an iPad with a hardware keyboard #161 (immersive). They overlap in purpose; which to keep is your call.

Problems found, and how they were fixed

• Dead code. A mutant that removed my "not over a keyboard" guard survived: over a keyboard, Larger Picture sets the picture's height anyway. The guard went.
• A blank VoiceOver action. A conditional action name would have left an empty-named action when nothing is hidden. It now uses accessibilityActions, with "Show the trackpad" only when it's hidden.
• Moved mutant. M3's pattern moved with the edit and was repointed.

Checks

• phone-portrait: 491 checks (7 new: the steps, the swipe rule, 273 phone sizes with the trackpad hidden: the picture takes all its room, the rows unchanged, nothing off the screen). 79 of 79 mutants (6 new).
• run-all.sh: all passed.
• The three iOS builds: Debug and Release for the simulator, Debug for a device.
• Harness photos on a private iPad Pro 13" simulator (iOS 27.0, deleted after): a 390×844 phone upright with and without the trackpad, the iPad upright without it, and sideways with everything hidden.

Not checked: the swipes and the edge swipe with a real finger (no touch rig was run), the grabber's 2 s, the Duo's halves, VoiceOver.

@Saffsanity: on the iPhone upright, swipe down on the buttons twice, then swipe up from the bottom edge. Sideways, swipe up on the bar, then down from the top.