refactor(core): move compute_time_bonus into scoring module

The win-time bonus is Ferrous house-rule scoring policy, not a bridge to
the upstream klondike crate, so it does not belong in klondike_adapter.
Relocate it to a dedicated solitaire_core::scoring module and update the
sole caller (win_summary_plugin) and the adapter/settings doc references.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

solitaire_core/src/scoring.rs

@@ -0,0 +1,15 @@
+//! Ferrous-specific scoring policy layered on top of upstream `klondike`.
+//!
+//! Upstream [`klondike::KlondikeStats::score`] owns the per-move point values
+//! (move-to-foundation, flip-up bonus, recycle penalty, etc.). The functions
+//! here are the Ferrous Solitaire house rules that upstream has no opinion on —
+//! currently just the win-time bonus shown in the win modal.
+
+/// Time bonus added to the score on a win: `700_000 / elapsed_seconds`.
+/// Returns 0 when `elapsed_seconds` is 0 to avoid division by zero.
+pub fn compute_time_bonus(elapsed_seconds: u64) -> i32 {
+    if elapsed_seconds == 0 {
+        return 0;
+    }
+    (700_000u64 / elapsed_seconds).min(i32::MAX as u64) as i32
+}