fix: cap cast progress at 100% after descent completion (bug #381)

Defense-in-depth fix across 2 files:

1. combat-descent-actions.ts: Added castProgress: 0 and weaponCastProgress: {}
   to the isDescentComplete set() call so the meter resets immediately.

2. combat-actions.ts: Added isDescentComplete to the early-exit guard in
   processCombatTick so combat processing stops entirely once descent is
   complete, preventing phantom spell casts from stale castProgress values.

All 1196 tests pass.

docs/dependency-graph.json

@@ -1,6 +1,6 @@
 {
   "_meta": {
-    "generated": "2026-06-12T16:57:07.675Z",
+    "generated": "2026-06-12T17:00:40.332Z",
     "description": "Import dependency graph for src/lib/game. Keys are files, values are arrays of files they import.",
     "usage": "To find what a file affects, search for its path in the VALUES. To find what a file depends on, look at its KEY entry."
   },