fix(contract): repair 3-arg LogPlayer callers + digest article bug

Three callers (main_window_shell.gd, narrate_harness.gd, npc_harness.gd)
still built LogPlayer with the OLD 3-arg shape (name, class_id,
luck_descriptor) after LogPlayer.new() was migrated to the 4-arg
(name, race_id, calling_id, luck_descriptor) shape. This was invisible
to both grep and the test suite: every ctor param carries a default, so
GDScript compiles a 3-arg call against a 4-arg signature without error —
it just silently mis-binds positionally. "sellsword" landed in the
race_id slot (rejected — not a race), the luck descriptor landed in the
calling_id slot (rejected — not a calling), and luck_descriptor itself
fell back to its default "". Every field in the emitted dict came out
empty, which 422s against the canon-log schema's minLength/enum
constraints. Grepping for class_id can't see this, because there is no
class_id token left anywhere — the bug is purely positional.

Also fixes prompts.py's _article(""), which returned "an" because
Python's "" in "aeiou" is True, producing a doubled-space/wrong-article
digest line when race_id is empty. _describe_player now builds its
descriptor from whichever of race/calling are present and omits the
clause entirely when both are absent.

Adds a schema-parity guard for origin.schema.json's inlined
allowed_callings enum, which duplicated the calling roster with no
runtime check tying it to Callings.IDS. Renames leftover "class"
vocabulary in test names/comments to "calling".

Regression coverage:
- client/tests/unit/test_entities.gd: ctor populates both race_id and
  calling_id; a calling passed into the race_id slot (the exact shape
  of the three broken call sites) yields an all-empty row.
- api/tests/test_prompts.py: empty-race and empty-race-and-calling
  digest rendering, asserting no doubled space and no dangling article.
- client/tests/unit/test_schema_parity.gd: origin.schema.json's
  allowed_callings enum matches Callings.IDS.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01QYa9u7Kdxv5gX4AnwWexy8

api/app/prompts.py

@@ -18,6 +18,8 @@ def _humanize(id_: str) -> str:
 
 
 def _article(word: str) -> str:
+    if not word:
+        return "a"
     return "an" if word[:1].lower() in "aeiou" else "a"
 
 
@@ -26,7 +28,11 @@ def _describe_player(player: dict) -> str:
     race = _humanize(player.get("race_id", ""))
     calling = _humanize(player.get("calling_id", ""))
     name = player.get("name", "")
-    return f"{name}, {_article(race)} {race} {calling}".strip()
+    parts = [p for p in (race, calling) if p]
+    if not parts:
+        return name
+    descriptor = " ".join(parts)
+    return f"{name}, {_article(parts[0])} {descriptor}".strip()
 
 
 @lru_cache(maxsize=None)