Show sharp tile preview labels and paths with tunnels and crossings

The mask labels under the tile preview sat inside the zoomed board.
Pixi rendered them at 10 px and stretched them with the zoom, and
each label was shrunk to the width of its tile on its own. They came
out blurry and in different sizes. The example map also only showed
a ring, so narrow paths and crossings were never previewed.

- The labels live in their own layer in screen space and are
  re-rendered at the fitting font size on every zoom.
- All labels share one size, at most the 10 px of the theme. Below
  6 px they are hidden.
- A label has two lines: the sides on top, the corners dimmed below.
- The example map keeps the ring cell for cell and adds a network of
  1 tile wide paths below it. It has straight 1xN and Nx1 pieces,
  curves, two T junctions, a crossing and a dead end.
- The map stands next to the grid in a wide panel and below it in a
  tall one. Fit picks the layout with the larger tiles, and only Fit
  changes it, so zooming does not make the board jump.
- The new hook __gm.tile.captions() reports size, scale and lines.

Found on the way: the taller map made Fit zoom out further, and 3
pixel checks on the 16 px terrain tiles failed. The side by side
layout fixed that.

Tests:
- ./check.sh: 160 files, 2364 tests, CHECK EXIT 0 (was 2363).
- e2e 39: ALL PASSED, 29 checks (was 28).
- New unit test: the example map has straights, a curve, a crossing
  with four notched corners, a T junction and a dead end.
- Counter check: with the labels back in the zoomed board the new
  caption check fails (scales [0.648, 1]).
- The e2e sum in the README is now 1381. It is calculated only.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

README.md

@@ -43,7 +43,7 @@ npm run build        # writes dist/ and regenerates index.html; the folder is wh
 The browser suite and the three example games need a machine with a GPU:
 
 ```bash
-node tools/seed-e2e.mjs && node tools/e2e.mjs      # the editor, 1380 checks (GM_STEPS=20 for one step)
+node tools/seed-e2e.mjs && node tools/e2e.mjs      # the editor, 1381 checks (GM_STEPS=20 for one step)
                                                    #   every tool signs in first – see the Accounts page
 node tools/seed-jumprun.mjs && node tools/smoke-jumprun.mjs
 node tools/seed-tetris.mjs && node tools/smoke-tetris.mjs