Add CONTD contract evaluator, deadline-aware buy pricing, actpkg JSON generator

- puga/contd.py, tools/contd.py: price open CONTD contract offers against real
  buy-fresh cost, flagging conditions that can't be priced from the API alone.
- tools/buyat.py: cheapest bid price likely to fill by a hard deadline
  (stockout risk), using the empirical first-passage model from history.py.
- puga/actpkg.py, tools/actpkg.py: Refined PrUn XIT ACT buy-list JSON packages.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

tools/actpkg.py

@@ -0,0 +1,40 @@
+#!/usr/bin/env python3
+"""Emit a Refined PrUn XIT ACT action-package JSON for a buy list - paste into the extension's
+"Import Action Package" (XIT ACT -> IMPORT) to pre-fill the CXPO buy tile for each material; you
+still click the real buy button yourself. See puga/actpkg.py for the schema/gotcha notes.
+
+  puga actpkg "Nike PP1 BDE buildout" BDE:3 BBH:3 BSE:4 MCG:76 PE:750
+  puga actpkg "Nike PP1 BDE buildout" BDE:3 BBH:3 BSE:4 MCG:76 PE:750 --cx AI1 -o nike_pp1.json
+"""
+import argparse, json, sys
+from pathlib import Path
+sys.path.insert(0, str(Path(__file__).resolve().parent.parent))
+from puga import config, actpkg
+
+
+def main():
+    ap = argparse.ArgumentParser()
+    ap.add_argument("name", help="package name (letters/digits/spaces only - punctuation is stripped)")
+    ap.add_argument("materials", nargs="+", help="TICKER:QTY pairs, e.g. BDE:3 MCG:76")
+    ap.add_argument("--cx", default=config.DEFAULT_CX)
+    ap.add_argument("-o", "--out", help="write to this file instead of stdout")
+    a = ap.parse_args()
+
+    mats = {}
+    for m in a.materials:
+        tk, _, qty = m.partition(":")
+        if not qty:
+            sys.exit(f"bad material spec {m!r}, expected TICKER:QTY")
+        mats[tk] = float(qty)
+
+    pkg = actpkg.build_package(a.name, mats, a.cx)
+    text = json.dumps(pkg, indent=2)
+    if a.out:
+        Path(a.out).write_text(text)
+        print(f"wrote {a.out}")
+    else:
+        print(text)
+
+
+if __name__ == "__main__":
+    main()