Clamp the lock screen's password field to the screen width

[SimonSchubert]

The lock screen's password field is wider than any screen narrower than it, so its outline and rounded corners are cut off on both sides.

LockView sets fieldWidth: 381, a fixed width on a field anchored centerIn: parent. At 360 logical the field runs from x = −11 to x = 370. Its left and right borders are off-screen, so it reads as a full-width band:

Before	After

The change

Clamp the field to the screen, less Style.gapsOut on each side. That's the same margin the polkit and reminder cards already leave with panel.width - Style.gapsOut * 2:

readonly property int fieldWidth: root.width > 0 ? Math.min(381, root.width - Style.gapsOut * 2) : 381

root.width is 0 until the lock surface is sized. The guard keeps the field at 381 until then, instead of a negative width.

Why it's safe

• On a desktop Math.min returns 381 and the field is unchanged.
• The password dots already shrink to fit passwordInput.width, which follows the field, so long passwords still stay visible in a narrower field.

Verification

Per agents/skills/visual-verification.md, reference and candidate captures of omarchy-shell lock preview:

• 720x1440 at scale 2 (360 logical): the field clamps to 350, with 5px on each side and its outline closed on all four sides. That's the "after" image above.
• 1920x1080 at scale 1: the field stays 381, and the capture matches the unpatched one to within 2/255 on 8 pixels, which is llvmpipe's anti-aliasing:

Desktop before	Desktop after

• Live switch between the two, in both directions: each matches a fresh start at the new size, and the journal is clean.

The VM runs a v4.0.3 shell, where LockView predates BackgroundMedia. To test this exact file rather than a backport, I added BackgroundMedia.qml and Util.isVideoPath from quattro for the test. The field code is identical in both versions.

A companion to #11034 and #11238, found the same way on a phone-shaped screen. Like those, it's a narrow-screen robustness fix rather than a mobile-specific one.