feat(data): expand challenge seed pool with 75 verified wins

Adds a gen_seeds binary to solitaire_assetgen that brute-searches seeds
for hands solvable in ≤250 moves, then writes the list.  The 75 new
seeds (0xCAFEBABE prefix) are appended to CHALLENGE_SEEDS in
solitaire_data::challenge.

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

solitaire_assetgen/src/bin/gen_seeds.rs

@@ -0,0 +1,157 @@
+//! Generate provably-winnable Klondike seeds for `CHALLENGE_SEEDS`.
+//!
+//! Walks seeds incrementally from `--start`, calls the solver on each, and
+//! collects only those that return `SolverResult::Winnable` (Inconclusive is
+//! rejected — the curated list wants proof). Prints Rust source suitable for
+//! pasting into `solitaire_data/src/challenge.rs`.
+//!
+//! # Usage
+//!
+//! ```bash
+//! cargo run -p solitaire_assetgen --bin gen_seeds --release -- \
+//!     --start 0xCAFE_BABE_0000_0000 --count 75
+//! ```
+//!
+//! Flags:
+//!   --start  Starting seed (decimal or 0x-prefixed hex, default 0xCAFEBABE00000000)
+//!   --count  Number of Winnable seeds to emit (default 75)
+//!   --help   Print this message
+
+use solitaire_core::game_state::DrawMode;
+use solitaire_core::solver::{try_solve, SolverConfig, SolverResult};
+
+fn main() {
+    let mut args = std::env::args().skip(1).peekable();
+    let mut start: u64 = 0xCAFE_BABE_0000_0000;
+    let mut count: usize = 75;
+
+    while let Some(arg) = args.next() {
+        match arg.as_str() {
+            "--start" => {
+                let val = args.next().unwrap_or_else(|| {
+                    eprintln!("error: --start requires a value");
+                    std::process::exit(1);
+                });
+                start = parse_u64(&val);
+            }
+            "--count" => {
+                let val = args.next().unwrap_or_else(|| {
+                    eprintln!("error: --count requires a value");
+                    std::process::exit(1);
+                });
+                count = val.parse().unwrap_or_else(|_| {
+                    eprintln!("error: --count must be a positive integer");
+                    std::process::exit(1);
+                });
+            }
+            "--help" | "-h" => {
+                eprintln!("{}", include_str!(concat!(env!("CARGO_MANIFEST_DIR"), "/src/bin/gen_seeds.rs")).lines().take(20).collect::<Vec<_>>().join("\n"));
+                return;
+            }
+            other => {
+                eprintln!("error: unknown argument: {other}");
+                std::process::exit(1);
+            }
+        }
+    }
+
+    if count == 0 {
+        eprintln!("error: --count must be > 0");
+        std::process::exit(1);
+    }
+
+    let cfg = SolverConfig::default();
+    let draw_mode = DrawMode::DrawOne;
+    let mut found: Vec<u64> = Vec::with_capacity(count);
+    let mut tried: u64 = 0;
+    let mut seed = start;
+
+    eprintln!(
+        "gen_seeds: finding {count} Winnable seeds from 0x{start:016X} (DrawOne) …"
+    );
+
+    while found.len() < count {
+        tried += 1;
+        if matches!(
+            try_solve(seed, draw_mode.clone(), &cfg),
+            SolverResult::Winnable
+        ) {
+            found.push(seed);
+            eprintln!(
+                "  [{:>3}/{}]  0x{:016X}  ({} tried so far)",
+                found.len(),
+                count,
+                seed,
+                tried
+            );
+        }
+        seed = seed.wrapping_add(1);
+    }
+
+    eprintln!("\nDone. Paste the block below into CHALLENGE_SEEDS in solitaire_data/src/challenge.rs:\n");
+
+    println!(
+        "    // Generated by solitaire_assetgen::gen_seeds \
+         (start=0x{start:016X}, count={count}, date={date})",
+        date = current_date()
+    );
+    for chunk in found.chunks(5) {
+        for s in chunk {
+            println!(
+                "    0x{:04X}_{:04X}_{:04X}_{:04X},",
+                (s >> 48) & 0xFFFF,
+                (s >> 32) & 0xFFFF,
+                (s >> 16) & 0xFFFF,
+                s & 0xFFFF,
+            );
+        }
+        println!();
+    }
+}
+
+fn parse_u64(s: &str) -> u64 {
+    let cleaned = s.replace('_', "");
+    if let Some(hex) = cleaned.strip_prefix("0x").or_else(|| cleaned.strip_prefix("0X")) {
+        u64::from_str_radix(hex, 16).unwrap_or_else(|_| {
+            eprintln!("error: could not parse '{s}' as a hex u64");
+            std::process::exit(1);
+        })
+    } else {
+        cleaned.parse().unwrap_or_else(|_| {
+            eprintln!("error: could not parse '{s}' as a decimal u64");
+            std::process::exit(1);
+        })
+    }
+}
+
+fn current_date() -> String {
+    use std::time::{SystemTime, UNIX_EPOCH};
+    let secs = SystemTime::now()
+        .duration_since(UNIX_EPOCH)
+        .map(|d| d.as_secs())
+        .unwrap_or(0);
+    let days = secs / 86400;
+    // Gregorian calendar computation (Tomohiko Sakamoto's algorithm variant)
+    let mut y = 1970u64;
+    let mut d = days;
+    loop {
+        let leap = (y.is_multiple_of(4) && !y.is_multiple_of(100)) || y.is_multiple_of(400);
+        let days_in_year = if leap { 366 } else { 365 };
+        if d < days_in_year {
+            break;
+        }
+        d -= days_in_year;
+        y += 1;
+    }
+    let leap = (y.is_multiple_of(4) && !y.is_multiple_of(100)) || y.is_multiple_of(400);
+    let month_days: [u64; 12] = [31, if leap { 29 } else { 28 }, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31];
+    let mut m = 0usize;
+    for &md in &month_days {
+        if d < md {
+            break;
+        }
+        d -= md;
+        m += 1;
+    }
+    format!("{y}-{:02}-{:02}", m + 1, d + 1)
+}