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>

solitaire_assetgen/src/bin/gen_art.rs

@@ -1,4 +1,4 @@
-//! Generates PNG assets for Solitaire Quest.
+//! Generates PNG assets for Ferrous Solitaire.
 //!
 //! Produces:
 //! - 52 card face PNGs (120×168) — one per card, with rank, suit symbol, and