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

client/scripts/newgame/new_game.gd

@@ -3,7 +3,7 @@ extends RefCounted
 ## New-game construction (spec "New-game construction"). Reads three immutable
 ## inputs (origin, world, creation) and writes two products (CanonLog, GameState).
 ## Nothing flows back up — charter §2 on the client. Validation is front-loaded:
-## a broken origin or illegal class fails here, loudly, not three scenes later.
+## a broken origin or illegal calling fails here, loudly, not three scenes later.
 
 static func construct(origin: Dictionary, world: ContentDB, creation: Dictionary, rng: RandomNumberGenerator) -> Dictionary:
 	var errors: Array = []