Specify Ta Yü ahead of building it, and list it as coming

Ta Yü has been out of print since the 2009 Goliath reissue, so the rulebook
had to be reconstructed from secondary sources — and this machine's network
policy blocks everything but search summaries, so BGG's rules files were out
of reach too.

The tile set fell out of the geometry rather than needing a component list.
A 1x3 tile has eight places a river mouth can sit; three mouths chosen from
eight gives 56 arrangements, and turning a tile end for end pairs them off
with no arrangement fixed, leaving exactly 28 distinct tiles. The reissue
has 84 tiles and the 1999 original had 112 — 3x28 and 4x28. Twelve of the 28
touch three flanks of the rectangle, which is what the ringed centre stud on
the reissued tiles marks. Three independent numbers agreeing is why the
geometry is worth trusting.

What could not be pinned down is called out in the doc rather than smoothed
over: the board is taken as 18x18 because that is the reading under which
"the four centre indentations" is true, the marked exits are placed at 3, 8
and 13 by choice, and the three-player flood variant is left out entirely
because nothing found says how the flood scores, and inventing that would be
shipping a different game. Same posture as the Sequence board layout.

The catalogue entry is added with available = false, so it shows as coming
soon on dev builds and stays out of production until the engine lands.

Co-Authored-By: Claude Opus 5 <[email protected]>
Claude-Session: https://claude.ai/code/session_015pyhC1KyFkQk6hUnnX2Tof

README.md

@@ -10,7 +10,7 @@ The app shell is complete and eight games are playable end to end:
 | | |
 | --- | --- |
 | **Playable** | Euchre, Kaiser, President, Golf, Wizard, Crazy 8s, Sequence, Chess |
-| **Listed, not yet implemented** | Mastermind, Backgammon, Checkers |
+| **Listed, not yet implemented** | Mastermind, Backgammon, Checkers, Ta Yü |
 
 Unimplemented games appear in the menu marked *Coming soon* **on dev builds
 only** — a production release lists just the games that can actually be played,
@@ -170,6 +170,9 @@ game:
 - [Wizard](docs/RULES-wizard.md)
 - [Crazy 8s](docs/RULES-crazy8s.md)
 - [Chess](docs/RULES-chess.md)
+- [Ta Yü](docs/RULES-tayu.md) — **not implemented yet**: this one is the
+  specification the engine will be written against, and it says which parts of
+  the out-of-print rulebook had to be reconstructed
 
 ## Layout