Rewrite Python comments in Google developer documentation style (#12)

* Rewrite comments in Google developer documentation style

Rewrite the comments and docstrings across the backend core modules so they
read plainly. The previous prose was accurate but dense and figurative, which
made it slow to skim.

Applies the Google developer documentation style guide: short sentences, active
voice, present tense, American spelling, and no metaphors, idioms, or
rhetorical asides. Replaces em-dash chains with separate sentences.

backend/tests/test_worldstate_integration.py

@@ -36,8 +36,9 @@ SCHEMA = {
     "milestones": {"win": {"desc": "Win the fight"}},
 }
 
-# The faked model narrates and appends a delta that exceeds the per-turn cap
-# (so we can see the engine clamp it), flips a flag, and completes a milestone.
+# The faked model narrates and appends a delta that exceeds the per-turn
+# cap, so the test can confirm the engine clamps it. It also flips a flag
+# and completes a milestone.
 AI_REPLY = (
     "The goblin's blade bites deep and Gwen nods at your resolve.\n\n"
     '```state\n{"player.hp": -80, "npc.gwen.trust": 15, "flags.alarm": true, "milestones.win": true}\n```'
@@ -131,7 +132,7 @@ def test_turn_applies_clamped_delta_and_strips_block(client):
     # The state block is not shown to the player.
     assert "```state" not in _last_ai_text(client.adv_id)
     assert "goblin's blade" in _last_ai_text(client.adv_id)
-    # ...but the raw model reply (with the block) is kept for the Insights view.
+    # The raw model reply, including the block, is kept for the Insights view.
     db = SessionLocal()
     try:
         snap = db.get(models.Adventure, client.adv_id).actions[-1].context_snapshot
@@ -175,7 +176,7 @@ def test_override_world_state_endpoint(client):
     # persisted to the DB, not just the response.
     assert _world(client.adv_id)["player"]["hp"] == 5
 
-    # bypasses max_delta_per_turn (30) — a direct correction, not a turn.
+    # This bypasses max_delta_per_turn (30) because it is a direct correction, not a turn.
     r = client.put(f"/api/adventures/{client.adv_id}/world-state", json={"player.hp": 100})
     assert r.json()["state"]["player"]["hp"] == 100