Report the world-state changes the engine refuses

`apply_delta` records three outcomes for every change the model sends:
`applied`, `clamped`, and `rejected`. Everything downstream read only
`applied`. A refused change reached the player as an ordinary chip, and
reached the model on the next turn as a change that had succeeded.

Five parts:

- `Action.world_changes` reads `clamped` and `rejected` beside `applied`.
  Accepted stats carry a `clamped` flag; refusals become `kind: "rejected"`
  entries. The `fix` key is present only when the engine wrote one, because
  this property runs for every action of every list response.
- The UI separates the three outcomes. A clamp to a standstill reads
  `no change - at its limit` on a dashed chip, a partial clamp is marked
  `(limited)`, and a rejection carries its reason. Dashed and dimmed rather
  than red: a refused change means the rules are working.
- The goals line names the milestone id, as `milestones.<id>`. The ids
  appeared nowhere in the prompt before, so the model could not send one.
- Each rejection, and each clamp that moved nothing, builds a `fix` string
  from the stat definition at the point of refusal. `render_refusals()`
  renders them into the next prompt above `EMIT_REMINDER`.
- `_history_text` replays `applied_delta()` instead of the sent delta, so a
  past turn's state block shows only what the engine accepted.

A clamp that reduced a change but still moved the value reports nothing. If
you tell a model its 80 damage became 30, it can treat the shortfall as a
debt and send the remaining 50 next turn, which is the swing
`max_delta_per_turn` prevents.

In the demo scenario, `pokemon_left` becomes `pokemon_fainted`
(`type: counter`, `initial: 0`). Starting at the ceiling turned a wrong-signed
delta into a silent no-op; counting up puts the wrong sign on the counter
rule, which refuses it out loud. The instructions also now ask for
`world.turn`, which sat at 0 for a whole playtest.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01PacdRuPXSkQQy4ZYdH32hF

backend/tests/test_egress.py

@@ -166,7 +166,7 @@ def test_world_changes_still_works_without_the_snapshot(client):
     ai = [a for a in r.json()["actions"] if a["type"] == "ai"]
     assert ai, "fixture should have AI actions"
     assert ai[0]["world_changes"] == [
-        {"kind": "stat", "label": "hp", "delta": -15, "value": 85}
+        {"kind": "stat", "label": "hp", "delta": -15, "value": 85, "clamped": False}
     ]