Clamp Anthropic temperature to [0.0, 1.0] in _build_anthropic_payload (#1737)

Anthropic's Messages API rejects temperature > 1.0 with HTTP 400, but
_build_anthropic_payload forwarded it verbatim. The shipped "Nietzsche" preset
uses temperature 1.2 and the UI slider allows up to 2.0, so every Claude request
under such a preset hard-broke. Clamp into [0.0, 1.0] in the Anthropic builder
only (OpenAI keeps its wider 0.0-2.0 range). Covers all three Anthropic call
paths, which build through this one function. None is passed through unchanged.

Fixes #1615

Co-authored-by: Ethan <23321960+0xLeathery@users.noreply.github.com>

tests/test_llm_core_anthropic_temp_clamp.py

@@ -0,0 +1,40 @@
+"""Regression guard for #1615 — Anthropic temperature must be clamped to [0.0, 1.0].
+
+Anthropic's Messages API rejects temperature > 1.0 with HTTP 400. The shipped
+"Nietzsche" preset uses temperature 1.2 (static/js/presets.js) and the UI slider
+allows up to 2.0 (static/index.html), so _build_anthropic_payload must clamp into
+[0.0, 1.0]. The clamp lives only in the Anthropic builder — OpenAI keeps its
+wider 0.0-2.0 range.
+"""
+import os
+
+os.environ.setdefault("DATABASE_URL", "sqlite:///:memory:")
+
+from src.llm_core import _build_anthropic_payload
+
+
+def _temp(t):
+    payload = _build_anthropic_payload(
+        "claude-x", [{"role": "user", "content": "hi"}], t, 100
+    )
+    return payload["temperature"]
+
+
+def test_above_range_is_clamped_to_one():
+    assert _temp(1.2) == 1.0  # the shipped "Nietzsche" preset — previously 400'd
+    assert _temp(2.0) == 1.0  # UI slider max
+
+
+def test_in_range_is_unchanged():
+    assert _temp(0.0) == 0.0
+    assert _temp(0.7) == 0.7
+    assert _temp(1.0) == 1.0
+
+
+def test_below_range_is_clamped_to_zero():
+    assert _temp(-0.5) == 0.0
+
+
+def test_none_is_passed_through_unchanged():
+    # Callers may pass None; behavior is unchanged (no clamp, no crash).
+    assert _temp(None) is None