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/circular-deps.txt

@@ -1,5 +1,5 @@
 # Circular Dependencies
-Generated: 2026-06-12T16:57:09.913Z
+Generated: 2026-06-12T17:00:42.616Z
 Found: 4 circular chain(s) — these MUST be fixed before modifying involved files.
 
 1. 1) data/guardian-encounters.ts > data/guardian-procedural.ts