feat: rotate the exported map by a bearing

[gmaclennan]

Adds a rotation setting so north need not be at the top of the print.
Tiles were already screen-space rects rendered as small MapLibre maps, and
MapLibre turns rigidly about the screen centre, so a bearing only changes
how a screen offset becomes a world point: tileGrid and the renderer's
edge-tile alignment turn their offsets by the bearing, and everything after
the renderer is untouched. The bbox is fitted north-up as before and the
page turns about its centre.

The hidden renderer map now passes a no-op transformConstrain: MapLibre's
default pans a camera whose unrotated frame crosses the latitude limit,
which would misalign an edge tile of a rotated page. fitsWorld checks all
four page corners instead. Raster layers can jog by up to a device pixel at
seams of a rotated page because MapLibre snaps them to whole world pixels
per map; this is documented rather than fixed.

The form gains a Rotation field, the preview map drag-rotates with a
compass and the two stay in sync, and the preview draws the page outline
alongside the bbox since the bbox corners can fall off a rotated page. The
e2e pages use a taller viewport so the longer form needs no scrolling,
which WebKit's checkbox click did not survive.

Closes #5

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Status	Name	Latest Commit	Preview URL	Updated (UTC)
✅ Deployment successful! View logs	map-printer	7b90257	Commit Preview URL Branch Preview URL	Sep 17 2026, 02:24 PM