chore: cargo fmt across workspace; add analytics domain to CSP

- Apply cargo fmt to solitaire_engine, solitaire_server formatting.
- solitaire_server/src/lib.rs: add https://analytics.aleshym.co to
  script-src, img-src, and connect-src so the analytics beacon loads
  without a CSP violation.
- docs and README updates.

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

solitaire_engine/Cargo.toml

@@ -52,3 +52,4 @@ web-sys       = { version = "0.3", features = ["Storage", "Window"] }
 [dev-dependencies]
 async-trait = { workspace = true }
 tempfile    = { workspace = true }
+solitaire_core = { workspace = true, features = ["test-support"] }