chore: rename app from Solitaire Quest to Ferrous Solitaire

Replace all display-name occurrences across web pages, Rust source,
docs, and Cargo metadata. Update localStorage token key from sq_token
to fs_token. Tagline "Klondike Solitaire" retained as genre descriptor.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

docs/ui-mockups/desktop-adaptation.md

@@ -3,7 +3,7 @@
 > **Why this exists.** The 24 mockups in this directory are mobile
 > (390 × 844 logical, iPhone 14 Pro frame) with one exception
 > (`home-menu-desktop.html`). The Stitch project that produced them
-> is named "Solitaire Quest *Mobile* Redesign" — the mobile-first
+> is named "Ferrous Solitaire *Mobile* Redesign" — the mobile-first
 > framing was deliberate when the new Android target opened, but
 > desktop is still the primary delivery surface. Porting the mobile
 > mockups 1:1 would land a 390-px-wide column floating in the middle