v0.7.6 — the solitaire door could not reach solitaire

Found by Jesse playing v0.7.5 on phoenix.local: a browser that had ever
held a multiplayer seat could not reach the new solitaire setup screen
at all. start() checked a browser-remembered multiplayer session before
ever looking at solitaire's own state, and a bare ./play.html load could
not tell "clicked Play solitaire" apart from "reloaded mid multiplayer
game" — the same problem ?lobby already solved for the door on the
other side, never applied to this one.

The door now links to ./play.html?solitaire, and start() treats that,
an explicit ?seed=, or the setup screen's own ?hand= (written by every
Deal) as proof this navigation means solitaire — checked ahead of the
remembered-session lookup rather than only below it.

862 tests pass, three new.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01AdG46Ja2PEDBkpqiDazMoX

src/web/index.html

@@ -79,7 +79,7 @@ footer{margin-top:26px;color:var(--dim);font-size:11px;display:flex;gap:18px;fle
       <span class="go" id="door-multiplayer-go">Set up a game &rarr;</span>
     </a>
 
-    <a class="door" href="./play.html">
+    <a class="door" href="./play.html?solitaire">
       <h2>Play solitaire</h2>
       <p>Play by yourself and run the entire division for five full days. Clear the Revenue floor of
          15 by the end or the game is a loss. Your game data is saved in your browser &mdash; if you close the tab and reopen this site