stop a flat top stamping its rim down the plateau

[Code-Grub]

Cliff tops get their rim line stamped across them several times instead of
once along the north edge. Clearest on the mound the Diglett's Cave mouth
is cut into on ROUTE_2, but it is on cliffs generally.

Top is dev, bottom is this branch, same camera.

Cause

A flat top fills its depth by cycling the first two drawn rows:

local m = math.min(2, run.extent)
local topTile = map:tileAt(tx, run.north + ((ty - run.north) % m))

That mound's rows are 1,17,17,17,17,17. Tile 1 is the top edge, tile 17
is the rock under it. Cycling two rows lays tile 1 again at ty12, ty14 and
ty16, so the rim turns up three times.

Fix

Where the drawing says the body is all one tile, lay the rim once and hold
the body after it. Art that really does repeat keeps cycling, which matters
for the Safari Zone fences: they alternate two tiles all the way down and
the repeat there is the drawing, not a bug.

Decided per column and per region, since each catches what the other
misses. The columns holding a cave mouth end in the mouth's own tiles, so
per column alone they kept cycling while their neighbours held and left rim
stubs above the doorway. A region vote alone silences a genuine
rim-over-body column sitting in a region of repeating art, of which the
Safari Zone has three. A column holds if either says so. Height is already
reconciled per region in the same function.

Checks

Swept all 222 maps. Of 3088 flat-topped runs, the 1336 rim-over-body ones
change and the other 1752 do not, so the fences and the short walls are
untouched.

• No geometry change. Comparing frames, nothing changed pixel touches the
  silhouette and no column's extent differs. Only the texel changes.
• tests/flat_top_test.lua fails if a rim-over-body run revisits an
  earlier row. 1336 failing on dev, 0 here.
• Safari fence and a Route 4 scene render pixel identical to dev.
• modkit validate and lint clean. SDK suite 1133/1150, same as dev.

Left the version and CHANGELOG alone so this does not collide with your
release PRs.

Not touched

The Fighting Dojo's walls are drawn on a four row period
(36,37,37,37,36,...) and the two row cycle gets those wrong too. Neither
holding nor cycling is right there so I left them alone rather than guess.

Also worth mentioning: every volume run in all 222 maps has rise = 0, so
the gable branch never runs on terrain and cliffs are flat boxes. That is
why a cave mouth reads square instead of sloping up to its top. Separate
problem, but happy to look at it.

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