The viewer uses the engine's projection, not the console's

It was drawing the map mirrored. The X flip came from the setup console's
picture of Brewer's Bane, which is an illustration and not a screenshot -
the game does not draw it that way round.

What the game does: L4GaugeImagePrimitive::Draw plots
MoveToAbsolute(dest->x, dest->z), so the screen axes are view-space X and
Z, and the graphics view's origin is bottom left with Y increasing upward
- BackgroundLine draws endpoints.bottomLeft to endpoints.topRight, and
the port's zero-degree blit is documented with the origin in the bottom
left corner. So +X runs right and +Z runs up.

Also added the heading the real display has. NavDisplay centres on the
vehicle and turns with it, inverting the viewer's transform and taking
yaw only unless rockAndRoll is set; the viewer defaults to heading 0,
which is the north-up case, and Q/E/R turn it. Panning and dragging now
work in what you see rather than in world axes, so up stays up when the
map is turned.

TRACKS.html is left following the console pictures on purpose: nine of
those cards are the console pictures, so the reconstructed nine have to
sit beside them consistently. The two disagree by a mirror and each is
right for what it is, which both READMEs now say.

tools/mapview/README.md

@@ -62,8 +62,20 @@ convenient nearby image.
 
 ## Orientation
 
-Seen from above with +Z up the page, the engine's +X runs to the **left**. The
-console's own picture of Brewer's Bane is what settles it: long leg up the right
-side to Score Zone 1, the corner, then the run out to Score Zone 2. Drawn the
-other way round every plan comes out mirrored, which is the bug this shares a
-fix with in [../pages/](../pages/).
+**+X runs right, +Z runs up.** That is the engine's projection rather than a
+choice. `L4GaugeImagePrimitive::Draw` plots `MoveToAbsolute(dest->x, dest->z)`,
+so the screen axes are view-space X and Z; and the graphics view's origin is at
+the bottom left with Y increasing upward — `BackgroundLine` draws
+`endpoints.bottomLeft` to `endpoints.topRight`, and the port's zero-degree blit
+is documented with the origin at the bottom-left corner.
+
+Worth knowing: **the setup console's pictures of the tracks are mirrored against
+this.** They are illustrations, not screenshots. The plans in `TRACKS.html`
+deliberately follow the console pictures, because nine of those cards *are* the
+console pictures and the reconstructed nine have to sit beside them consistently.
+This viewer follows the game instead. The two disagree by a mirror, and both are
+right for what they are.
+
+The nav display also centres on the vehicle and turns with it, inverting the
+viewer's transform and taking yaw only unless `rockAndRoll` is set. Heading 0
+here is the north-up case; <kbd>Q</kbd>/<kbd>E</kbd> turn the map.